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PRACTICAL TREATISE 



ON 



GEARING. 



BROWN & SHARPE MFG. CO. 



Providence, R. I., U. S. A, 




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eo >-( 

IS 



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PRACTICAL TREATISE 



ON 



GEARING. 



X._...v 



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fourth: edition. 



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PROVIDENCE, R. I. 

BROWN & SHARPE MANUFACTURING COMPANY. 

1893. 






Entered according to Act of Congress, in the year 1893 by 

BROWN & SHARPE MFG. CO., 

In the Office of the Librarian of Congress at Washington. 

Registered at Stationers' Hall, London, Eng. 

All rights reserved. 

] 



(I 



'V 




PREFACE. 



This Book is made for men in practical life ; for those who 
would like to know how to construct gear wheels, but whose 
duties do not afford them sufficient leisure for acqumng a 
technical knowledge of the subject. 



CONTENTS 



PART I. 

Chapter I. 



PAGE, 

Pitch Circle — Pitch — Tooth — Space — Addendum or Face — 

Flank — Clearance 1 

Chapter II. 
Classification — Sizing Blanks and Tooth Parts from Circular 

Pitch — Center Distance » 6 

Chapter III. 
Single Curve Gears of 30 Teeth and over 9 

Chapter IV. 
Rack to Mesh with Single Curve Gears having 30 Teeth and 

over 12 

Chapter V. 
Diametral Pitch — Sizing Blanks and Teeth — Distance between 

Centers of Wheels 16 

Chapter VI. 
Single-Curve Gears, having Less than 30 Teeth — Gears and 

Racks to Mesh with Gears having Less than 30 Teeth. . . 20 

Chapter VII. 
Double-Curve Teeth— Gear of 15 Teeth— Rack 25 

Chapter VIII. 
Double-Curve Gears, having More and Less than 15 Teeth — 

Annular Gears 30 

Chapter IX. 
Bevel Gear Blanks 34 

Chapter X. 
Bevel Gears— Form and Size of Teeth— Cutting Teeth 40 



VI CONTENTS. 

Chapter XI. 

PAGE, 

Worm Wheels — Sizing Blanks of 32 Teeth and over. 44 

Chapter XII, 

Sizing Gears when the Distance between Centers and the 
Katio of Speeds are fixed — General Remarks — Width of 
Face of Spur Gears— Speed of Gear Cutters— Table of 
Tooth Parts 59 



PART II. 

Chapter I. 
Tangent of Arc and Angle 73 

Chapter II. 

Sine, Cosine and Secant — Some of their Apphcations in 

Machine Construction 79 

Chapter III. 

Application of Circulur Functions — Whole Diameter of Bevel Grear 
Blanks — Angles of Bevel G-ear Blanks 84 

Chapter IV 
Spiral Gears — Calculations for Pitch of Spirals 91 

Chapter V. 
Examples in Calculations of Pitch of Spirals — Angle of 
Spiral — Circumference of Spiral Gears — A few Hints on 
Cutting 95 

Chapter VI. 
Normal Pitch of Spiral Gears — Curvature of Pitch Surface — 

Formation of Cutters 100 



CONTENTS. VU 

* 

Chapter VII. 

PAGE. 

Screw Gears and Spiral Gears — General Remarks 106 

Chapter VIII. 

Continued Fractions — Some Applications in Machine Con- 
struction 108 

Chapter IX. 
Angle of Pressure 113 

Chapter X. 
Internal Gears — Tables — Index 115 

Chapter XL, 
Strength of aears— Tables , _ , . 118 



I N DEX 



A. 

PAGE. 

Abbreviations of Parts of Teeth and Gear^ 4 

Addendum 2 

Angle, How to Lay Off an 74, 89 

Increment 88 

of Edge 84 

of Face 84 

of Pressure , 112 

of Spiral 94 

Angular Yelocity 1 

Annular Gears 32, 1 15 

Arc of Action 114 

B. 

Base Circle 11 

" of Epicycloidal System 25 

" of Internal Gears 115 

Bevel Gear Blanks 34 

" Angles by Diagram. 36 

" " by Calculation 84, 88 

" Form of Teeth of 40 

» Whole Diameter of 37, 86 

C. 

Centers, Line of 2 

Circular Pitch 4 

Classification of Gearing 5 

Clearance at Bottom of Space 6 

" in Pattern Gears 8 

Condition of Constant Velocity Ratio 2 

Contact, Arc of 114 

Continued Fractions 108 

Coppering Solution 65 



INDEX. IX 

PAOB. 

Cutters, How to Order 63 

" Table of Epicycloidal 64 

'* of Involute 62. 

" " of Speeds for 61 

D. 

Decimal Equivalents, Tables of 119, 126 

Diameter Increment 86 

" of Pitch Cii'cle 6 

" Pitch 5 

Diametral Pitch 17 

Distance between Centers o 8 

E. 

Elements of Gear Teeth 5 

Epicycloidal Gears, with more and less than 15 Teeth 30 

" with 15 Teeth 25 

Hack 27 

F. 

Face, Width of Spur Gear 60 

Flanks of Teeth in Low-numbered Pinions 20 

G. 

Gear Cutters, How to Order 63 

" Patterns 8 

Gearing Classified 5 

Gears, Bevel 34, 85, 86 

" Epicycloidal 25 

" Involute 9 

" Spkal 91 

» Worm 44 

H. 

Herring-bone Gears 107 

I. 

Increment, Angle 88 

" Diameter 86 

Interchangeable Gears 24 

Internal or Annular Gears 115 

Involute Gears, 30 Teeth and over 9 

" '' with Less than 30 Teeth 20 

Rack 12 



INDEX. 

L. 



PAGE. 



Limiting Numbers of Teeth in Internal Gears 32 

Line of Centers 2 

" of Pressure 12, 113 

Linear Telocity 1 

N. 

Normal 100 

" Helix 100 

" Pitch 100 

O. 

Odontograph, Willis 117 

Original Cylinders 1 



Pattern Gears 8 

Pitch Circle 3 

" Circular or Linear 4 

" a Diameter 6 

" Diametral 17 

" Normal 100 

" of Spirals 94 

Polygons, Calculations for Diameters of - 81 

E. 

Rack 12 

" for Epicycloidal Gears 27 

*' for Involute " 12 

" for Spiral " 105 

Relative Angular Telocity 2 

Rolling Contact of Pitch Circle 3 

S. 

Screw Gearing 91, 107 

Single-Curve Teeth 9 

Speed of Gear Cutters 61 

Spiral Gearing 91 

Standard Templets 27 

Strength of Gears 118 



INDEX. XI 

T. 



PAGE. 



Table of Decimal Equivalents 119, 126 

" of Sines, etc 120 

" of Speeds for Gear Cutters 61 

« of Tooth Parts 68 

V. 

Velocity, Angular 2 

" Linear 1 

« Kelative 2 

W. 

Wear of Teeth 60, 107 

"WilHs Odontograph 117 

"Worm Gears , 44 



PART I. 



CHAPTER I. 

PITCH CIRCLE, PITCH, TOOTH, SPACE, ADDENDUM OR FACE, FLASK, 

CLEARANCE. 



Let two cylinders, Fig. 1, touch each other, their j^^efg*^^^ ^^^' 
axes be parallel and the cylinders be on shafts, turning 
freely. If, now, we turn one cylinder, the adhesion of 
its surface to the surface of the other cylinder will 
make that turn also. The surfaces touching each 
other, without slipping one upon the other, will evi- 
dently move through the same distance in a given 
time. This surface speed is called linear velocity. 



Linear Veloci- 
ty. 



TANGENT CYLINDERS. 




Fig. 1 

LiNEAK Velocity is the distance a point moves along 
a line in a unit of time. 

The line described by a point in the circumference 
of either one of these cylinders, as it rotates, may be call- 
ed an arc. The length of the arc (which may be greater 
or less than the circumference of cylinder), described 
in a unit of time, is the velocity. The length, expressed 
in linear units, as inches, feet, etc., is the linear velocity. 



BROWN & SHAEPE MFG. CO. 

The length, expressed in angular units, as degrees, is 
the angular velocity. 

If now, instead of 1° we take 360°, or one turn, as 
and 1 minute as the time unit, the 
angular velocity will be expressed in turns or revolu- 
tions per minute. 

If these two cylinders are of the same size, one will 
make the same number of turns in a minute that the 
other makes. If one cylinder is twice as large as the 
other, the smaller will make two turns while the larger 
makes one, but the linear velocity of the surface of 
each cylinder remains the same. 

This combination would be very useful in mechan- 
ism if we could be sure that one cylinder would always 
turn the other without slipping. 



i^A^g^^ar ve. ^-^^ angular unit. 



Relative An- 
gular Velocity. 




'Fi^y. S 



^o0-^-S^ 




C/fiCLE 



Land. 

Addendum. 

Tooth. 

Gear. 

Train. 



In the periphery of these two cylinders, as in Fig. 
2, cut equidistant grooves. In any grooved piece the 
places between grooves are called lands. Upon the 
lands add parts ; these parts are called addenda. A 
land and its addendum is called a tooth. A toothed 
cylinder is called a gear. Two or more gears with 
teeth interlocking are called a trahi. A line, c c', Fig. 



PROVIDENCE, R. I. 



3 



Addendum 
Circle. 



2 or 3, between tlie centers of two wheels is called the Lij^^ of cen 
line of centers. A circle just touching the addenda 
is called the addendwm circle. 

The circumference of the cylinders without teeth is 
called the pitch circle. This circle exists geometri- ^^*^^ ^^^^^®- 
cally in every gear and is still called the pitch circle ^.^^^^ circle 
or the primitive circle. In the study of gear wheels, it the^^ PriStive 
is the problem to so shape the teeth that the pitch Circle, 
circles will just touch each other without slipping. 

On two fixed centers there can turn only two circles, 
one circle on each center, in a given relative angular 
velocity and touch each other without slipping. 




Fig.<L 



4 , BROWN & SHARPE MFG. CO. 

Space. The groove between two teeth is called a space. 

In cut gears the width of space at pitch line and thick- 
ness of tooth at pitch line are equal. The distance 
between the center of one tooth and the center of the 

Circular Pitcii. next tooth, measured along the pitch line, is the cir- 
cular pitch; that is, the circular pitch is equal to a 
Tooth Thick- tooth and a space : hence, the thickness of a tooth at 

ness. ^ 

the pitch line is equal to one-half the circular pitch. 
ti<ms^of Spirts -^^^ D= diameter of addendum circle. 

for Teeth and a J)'=: " ' " pitch " 

" P'=: circular pitch. 

" ^=: thickness of tooth at pitch line. 

*' 5= addendum or face, also length of working 

part of tooth below pitch line or flank. 
" 2s=jy" or twice the addendum, equals the 

working depth of teeth of two gears in 

mesh. 
" y= clearance or extra depth of space below 

working depth. 
" s-f-Z^: depth of space below pitch line. 
** D"+y*= whole depth of space. 
" N= number of teeth in one gear. 
" ;r=3.1416 or the circumference when diameter 

is 1. 
P' is read "P prime.'' D" is read "D second." 
7t is read, " pi." 

If we multiply the diameter of any circle by tt, the 
To find the product will be the circumference of this circle. If 
and Diameter we divide the circumference of any circle by 7t, the 
quotient will be the diameter of this circle. 



PBOVIBENCE, K. I. 



CHAPTER 11. 

CLASSIFICATION— SIZING BLANKS ADD TOOTH PARTS FROM 
CIRCULAR PITCH— CENTER DISTANCE— PATTERN GEARS. 



If we conceive the pitch of a pair of gears to 1^© the^ TeeS?^ ^' 
made the smallest possible, we ultimately come to the 
conception of teeth that are merely lines upon the 
original pitch surfaces. These lines are called ele- 
ments of the teeth. Gears may be classified with 
reference to the elements of their teeth, and also with 
reference to the relative position of their axes or -shafts. 
In most gears the elements of teeth are either straight 
lines or helices (screw-like lines). 

In Paet I. of this work, we shall treat upon three 

KINDS OF GEARS t 

First — Spur Gears ; those connecting parallel shafts ^p^^ Gears, 
and whose tooth elements are straight. 

Second — Bevel Gears; those connecting shaf ts ^e'^®^ ^®*^3- 
whose axes meet when sufficiently prolonged, and the 
elements of whose teeth are straight lines. In bevel 
gears the surfaces that touch each other, without 
slipping, are upon cones or parts of cones whose 
apexes are at the same point where axes of shafts meet. 

Third — Screw or Worm Gears; those connecting ^^^^ ®J^^^^^^ 
shafts that are neither parallel nor meet, and the ele- 
ments of whose teeth are helical or screw-like. 

The circular pitch and number of teeth in a wheel g_^^ 
being given, the diameter of the wheel and size of Blanks, &o. 
tooth parts are found as follows : 

Dividing by 3.1416 is the same as multiplying by 
rrire- ^^^ g^^^^ — .3183; hence, multiply the cir- 
cumference of a cn-cle by .3183 and the product will be 
the diameter of the circle. Multiply the circular pitch 
by .3183 and the product will be the same part of the 



6 BEOWN & SHARPE MFG. CO. 

diameter of pitch circle that the circular pitch is of the 

circumference of pitch circle. This part or modulus 
A Diameter ig called a diameter pitch. There are as many diameter 

pitches contained in the diameter of pitch circle as 

there are teeth in the wheel. 
A Diameter Most mechanics make the addendum of teeth equal 

Fitch and, tne ^ 

Addendum to one diameter pitch. Hence we can designate this 

measure the ^ o 

same, radially, modulus or diameter pitch by the same letter as we da 

the addendum ; that is, let « = a diameter pitch. 

.3183 V — s, or circular pitch multiplied by .3183=«, 

or a diameter pitch. 

Ns=D', or number of teeth in a wheel, multiplied 

PiSh^ircie ^^ ^^ ^ diameter pitch, equals diameter of pitch circle. 

(N + 2) s=D, or add 2 to the number of teeth, mul- 

Whoie Diam- tiplv the sum bv s and product will be the whole 
eter. ^- . 

diameter. 

1 =/, or one tenth of thickness of tooth at pitch-line 
Clearance. equals amount added to bottom of space for clearance. 
Some mechanics prefer to make/ equal to -jig- of the 
working depth of teeth, or .0625 D''. One-tenth of 
the thickness of tooth at pitch-line is more than one- 
sixteenth of working depth, being .07854 D". 
Example. Example.— Wheel 30 teeth, If' circular pitch. 

Size fBiank'^'"^'^ ' ' ^"'^^^ t—.l^" or thickness of tooth equals f". 
and Tooth 5=1.5''X.3183— .4775"=:a diameter pitch. (See 

parts for Gear •*■ ^ 

Of 30 teeth, i><r tables of tooth parts, pages 68-71). 

in. circular ^ x o / 

pitch. D'=30X.4775" = 14.325"=diameter of pitch-circle. 

D=(30+2)X.4775" = 15.280"=diameter of adden- 
dum circle. 

f=^ of .75'' =.075"= clearance at bottom of space. 

D"=2x.4775"=.9549"=working depth of teeth. 

D" + /n:2x.4775"-f.075''=1.0299''=whole depth of 
space. 

5-|-/=.4775"-F.075''=.5525"=depth of space inside 
of pitch-line. 

D"=2s or the working depth of teeth is equal to 
two diameter pitches. 

In making calculations it is well to retain the fourth 
place in the decimals, but when drawings are passed 
into the workshop, three places of decimals are suffi- 
cient. 



PROVIDENCE, R. I. 




Fig. 5, Spue Gearing. 



8 BROWN & SHAEPE MFG. CO. 

ivroen^^^nters ^^^ distance between the centers of two wheels is 

Df two Gears, evidently equal to the radius of pitch-circle of one wheel 

added to that of the other. The radius of pitch-circle 

is equal to s multiplied by one-half the number of teeth 

in the w^heel. 

Hence, if we know the number of teeth in two wheels, 
in mesh, and the circular pitch, to obtain the distance 
between centers we first find s ; then multiply s by one- 
half the sum of number of teeth in both wheels and the 
product will be distance between centers. 

Example. — What is the distance between the centers 
of two wheels 35 and 60 teeth, IJ" circular pitch. "We 
first find s to be IJ^x .3183=.3979". Multiplying by 
47.5 (one-half the sum of 35 and 60 teeth) we obtain 
18.899" as the distance between centers. 
Shr\'Sk?gI*S Pattern. Gears should be made large enough to 
Gear Castings, allow for shrinkage in casting. In cast-iron the shrinkage 
is about ^ inch in one foot. For gears one to two feet 
in diameter it is well enough to add simply ^dt ^^ 
diameter of finished gear to . the pattern. In gears 
about six inches diameter or less, the moulder -will 
generally rap the pattern in the sand enough to make 
any allowance for shrinkage unnecessary. In pattern 
gears the spaces between teeth should be cut wider 
than finished gear spaces to allow for rapping and to 
avoid having too much cleaning to do in order to have 
gears run freely. In cut patterns of iron it is generally 
Metal Pattern enough to make^spaces .015" to .02" wider. This 
makes clearance .03'' to .04" in the patterns. Some 
moulders might want .06" to .07" clearance. 

Metal patterns should be cut straight ; they work 
better with no draft. It is well to leave about .005" to 
be finished from side of patterns after teeth are cut ; 
this extra stock to be taken away from side where 
cutter comes through so as to take out places where 
eto3k is broken out. The finishing should be done 
with file or emery wheel, as turning in a lathe is likely 
to break out stock as badly as a cutter might do. 

If cutters are kept sharp and care is taken when 
coming through the allowance for finishing is not nec- 
essary and the blanks may be finished before they are 
cut. 



PROVIDENCE, R. I. 



CHAPTER III. 
SIHGLE-CDRYE GEARS OF 30 TEETH AHD OYER. 



Single-cui've teeth are so called because they have rj^^l^g}^ ^^^^ 
but one cm-ve by theory, this curve forming both face 
and flank of tooth sides. In any gear of thirty teeth 
and more, this cui've can be a single arc of a circle 
whose radius is one-fourth the radius of the pitch 
circle. In gears of thu'ty teeth and more, a fillet is 
added at bottom of tooth, to make it stronger, equal 
in radius to one-sixth the widest part of tooth space. 

A cutter formed to leave this fillet has the advantage 
of wearing longer than it would if brought up to a 
comer. 

In geai's less than thirty teeth this fillet is made the 
same as just given, and sides of teeth are formed with 
moi'« than one arc, as will be shown in Chapter YI. 

Having calculated the data of a gear of 30 teeth, f Example of a 
inch cii'cular ]3itch (as we did in Chapter II. for 1^" =x"' 
pitch), we proceed as follows : 

1. Draw pitch ciixle and point it off into parts equal Geometrical 

. 1 IP ,1 • 1 •, 1 Construction. 

to one-nali the circular pitch. Fig. 6. 

2. From one of these points, as at B, Fig. 6, draw 
radius to pitch circle, and upon this radius describe a 
semicircle ; the diameter of this semicircle being equal 
to radius of pitch circle. Draw addendum, working 
depth and whole depth cu'cles. 

3. From the point B, Fig. 6, where semicircle, pitch 
cii'cle and outer end of radius to pitch circle meet, lay 
off a distance upon semicircle equal to one-fourth the 
radius of pitch circle, shown in the figure at BA, and 
is laid off as a chord. 

4. Through this new point at A, upon the semicircle, 
draw a circle concentric to pitch cu'cle. This last is 



10 



BKOWN & SHARPE MFG. CO. 



'Fi^.G 






o 
tr 
o 




i 

o. 


GEAR, 30 TEETH, 


11. 


^'CIRCULAR PITCH, 


o 


P'=|.''or,75'" 


CO 


N=30 


D 


P =4.1888' 


^ 


t = .375" 




S= .2387- 




D"= .4775' 




S^f= .2762' 




D"+/-= .5150' 




D' =7.1610" 




D ^7.6384" 





SINGLE CURVE GEAR. 



PROVIDENCE, R. I. 11 

called the base circle, and is the one for centers of 
tooth arcs. In the system of single curve gears, v^e 
have adopted, the diameter of this circle is .968 of the 
diameter of pitch circle. Thus the base circle of any 
gear 1 inch pitch diameter by this system is .968". 
If the pitch cii'cle is 2" the base circle will be 1.936." 

5. "With dividers set to one-quarter of the radius of 
pitch circle, draw arcs forming sides of teeth, placing 
one leg of the dividers in the base circle and letting 
the other leg describe an arc through a point in the 
pitch circle that was made in laying off the parts equal 
to one-half the circular pitch. Thus an arc is drawn 
about A as center through B. 

6. With dividers set to one-sixth of the widest part 
of tooth space, draw the fillets for strengthening teeth 
at their roots. These fillet arcs should just touch the 
whole depth circle and the sides of teeth already 
described. 

Single curve or involute gears are the only gears jj^-^Qi^^^^gg^jf 
that can run at varying distance of axes and transmit ^^^• 
unvarying angular velocity. This peculiarity makes 
involute gears specially valuable for driving rolls or 
any rotating pieces, the distance of whose axes is 
likely to be changed. 

The assertion that gears crowd harder on bearings Pressure on 

^ ^ bearings. 

when of involute than when of other forms of teeth, 
has not been proved in actual practice. 

Before taking next chapter, the learner should make Practice, be- 
several drawings of gears 30 teeth and more. Say next chapter. 
make 35 and 70 teeth 1^" P'. Then make 40 and 65 
teeth J" P'. 

An excellent practice will be to make drawing on 
cardboard or Bristol-board and cut teeth to lines, thus 
making paper gears ; or, what is still better, make them 
of sheet metal. By placing these in mesh the learner 
can test the accuracy of his work. 



12 ' BBOWN & SHAKPB MFG. CO. 



CHAPTER IV. 

RACK TO MESH WITH SINGLE-CDRYE GEARS HAYING 
30 TEETH AKD OYER. 



made" ^re \ra- "^^^^ ^^^^ (^^S- '^) ^^ Hiade precisely the same as gear 
ton^ to drawing {j^ Chapter III. It makes no difference in which direc- 
tion the construction radius is drawn, so far as obtain- 
ing form of teeth and making gear are concerned. 

Here the radius is drawn perpendicular to pitch line 
of rack and through one of the tooth sides, B. A semi- 
circle is drawn on each side of the radius of the pitch 
circle. 

The points A and A' are each distant from the point 
B, equal to one-fourth the radius of pitch circle and 
correspond to the point A in Fig. 6. 

In Fig. 7 add two lines, one passing through B and 
A and one through B and A^ These two lines form 
angles of 75 J° (degrees) with radius BO. Lines BA 
and BA' are called lines of pressure. The sides of 
rack teeth are made perpendicular to these lines. 
Rack. A Rack is a straight piece, having teeth to mesh 

with a gear. A rack may be considered as a gear of 
infinitely long radius. The circumference of a circle 
approaches a straight line as the radius increases, and 
when the radius is infinitely long any finite part of the 
Construction circumference is a straight line. The pitch line of a 

of Pitcli Line of . ° . ■, -, 

Kack. rack, then, is merely a straight Ime just touchmg the 

pitch circle of a gear meshing with the rack. The 
thickness of teeth, addendum and depth of teeth 
below pitch line are calculated the same as for a wheel. 
(For pitches in common use, see table of tooth parts.) 
The term circular pitch when applied to racks can be 
more accurately replaced by the term linear pitch. Linear 
applies strictly to a line in general while circular pertains to a 
circle. Linear pitch means the distance between the centres 
of two teeth on the pitch line whether the line is straight or 
curved. 



PROVIDENCE, R. I. 



13 



A rack to mesh with a smgle-curve gear of 30 teeth 
or more is drawn as follows : 

1. Draw straight pitch line of rack ; also draw ad- 
dendum line, working depth line and whole depth line, 
each pai-allel to the pitch line (see Fig. 7). 



Eack. 
Fig. 7. 



O 



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A' 












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i^ 












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t \ 


s: 














fe 












O 

CO 


CO 






- 






3 


3 












Q 


o 












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\ ^ 












5 / 








^—li^ 






^ / 


V 




^ 


7"\ 






i/ / / 




=4 


f — ^ 




^ 




/ 


'^^^I^^^V'^ A D D E N DLTmI 1 N E 




s^ 






P 




J I \ \ PITCH LINE 




^^^R 




/ 


S/t 


\ -^1 






\ 


^7 \ 




^"^^ 1 


W 


\\__^ WORKI 


h 


DEPTH LINE \ 






WHOLE DEPTH LINE / 






RACK 3^" ( 


;|RCULAR PITCH. 






; 





















RACK TO MESH WITH SINGLE CURVE GEAR 
HAVING 30 TEETH AND OVER. 



14 BEOWN & SHAKPE MFG. CO. 

2. Point off the pitch line into parts equal to one- 
half the circular pitch, or =^. 

3. Through these points draw lines at an angle of 
75^° with pitch lines, alternate lines slanting in oppo- 
site directions. The left-hand side of each rack tooth 
is perpendicular to the line BA. The right-hand side 
of each rack tooth is perpendicular to the line BA'. 

4. Add fillets at bottom of teeth equal to |- of the 
width of spaces between the rack teeth at the adden- 
dum line. 

sides ^of^ -Rail ^^^ sketch. Fig. 8, will show how to obtain angle of 
Teeth. sides of rack teeth, directly from pitch line of rack, 

without drawing a gear in mesh with the rack. 




Upon the pitch line b b', draw any semicircle — 
baa' b'. From point b lay off upon the semicircle 
the distance b a, equal to one-quarter of the diameter 
of semicircle, and draw a straight line through b and a. 

This line, b a, makes an angle of 75|° with pitch line 
bb', and can be one side of rack tooth. The same 
construction, b' a', will give the inclination 75^° in the 
opposite direction for the other side of tooth. 

The sketch. Fig. 9, gives the angle of sides of a tool 
for planing out spaces between rack teeth. Upon any 
line OB draw circle OABA'. From B lay off distance 
BA and BA', each equal to one-quarter of diameter of 
the circle. 

Draw lines OA and OA'. These two lines form an 
angle of 29°, and are right for inclination of sides of 
rack tool. 



PROVIDENCE, E. I. 1 O 

Make end of rack tool .31 of ckcular pitch, and then width of Rack 



Tool at end. 



round the corners of the tool to leave fillets at the 
bottom of rack teeth. 

Thus, if the circular pitch of a rack is IJ" and we 
multiply by .31, the product .465" will be the width of 
tool at end for rack of this pitch before corners are 
taken off. This width is shown at x y. 




This sketch and the foregoing rule are also right for worm Thread 
a worm-thi'ead tool, but a worm-thread tool is not 
usually rounded for fillet. In cutting worms, leave 
width of top of thread .335 of the circular pitch. 
"When this is done, the depth of thread will be right. 




16 BROWN & SHAKPE MFG. CO. 



CHAPTER V. 

DIAMETRAL PITCH— SIZIHG BLANKS AND TEETH— DISTANCE 
BETWEEN CENTERS OF WHEELS. 



, . In making drawings of gears, and in cutting racks, 
necessary to it is necessarv to know the circular pitch, both on 

know the Cir- 

cuiar Pitch. account of Spacing teeth and calculating their strength. 
It would be more convenient to express the circular 
pitch in whole inches, and the most natural divisions 
inacompieteof an inch, as V P', f" P', ^" P', and so on. But as 
Pitch ^circum- the circumf erence of the pitch circle must contain the 
conSrfth?ciT- circular pitch some whole number of times, corre- 
some whole sponding to the number of teeth in the gear, the 
Smes.^^^ ^^ diameter of the pitch circle will often be of a size not 
readily measured with a common rule. This is because 
the circumference of a circle is equal to 3.1416 times 
the diameter, or the diameter is equal to the circum- 
ference multiplied by .3183. 

In practice, it is better that the diameter should be 
Pitch, in of some size conveniently measured. The same applies 

Terms of the _ -^ ^ ^ ^^ 

Diameter. to the distance between centers. Hence it is generally 
more convenient to assume the pitch in terms of the 
diameter. In Chapter II. was given a definition of a 
diameter pitch, and also how to get a diameter pitch 
from the circular pitch. 

We can also assume a diameter pitch and pass to its 
Circular Pitch equivalent circular pitch. If the circumference of the 

and a Diame- •'■ ^ 

ter Pitch. pitch circle is divided by the number of teeth in the 
gear, the quotient will be the circular pitch. In the 
same manner, if the dia?neter of the pitch circle is 
divided by the number of teeth, the quotient will be a 
diameter pitch. Thus, if a gear is 12 inches pitch 
diameter and has 48 teeth, dividing 12" by 48, the 
quotient J" is a diameter pitch of this gear. In prac- 



PROVIDENCE, R. I. 17 

tice, a diameter pitch is taken in some convenient part 

of an inch, as i" diameter pitch, and so on. It Abbreviation 

. ' 1 ■■ . -, of Diameter 

IS convement m calculation to designate one of these Pitch. 
diameter pitches by s, as in Chapter II. Thus, for ^" 
diameter pitch, s is equal to ^". Generally, in speak- 
ing of diameter pitch, the denominator of the fraction 
only is named. J" diameter pitch is then called 3 
diametral pitch. That is, it has been found more con- 
venient to take the reciprocal of a diameter pitch in 
making calculation. The reciprocal of a number is 1, 
divided by that number. Thus the reciprocal of J is a NuiSJei?*^ ^ 
4, because \ goes into 1 four times. 

Hence, we come to the common definition : 

Diametral Pitch is the number of teeth to one inch pitch."^^ ^^ 
of diameter of pitch circle. Let this be denoted by P. 
Thus, J" diameter pitch we would call 4 diametral 
pitch or 4 P, because there would be 4 teeth to every 
inch in the diameter of pitch circle. The circular 
pitch and the different parts of the teeth are derived 
from the diametral pitch as follows. 

i^L^ = p' or 3.1416 divided by the diametral pitch Given theDi- 

■^ ^ X ametral to find 

is equal to the circular j)itch. Thus to obtain the cir-ti^^ circular 
culai- for 4 diametral pitch, we divide 3.1416 by 4 and 
get .7854 for the circular pitch, corresponding to ^^^f^^^^p^^^^!^ 
diametral pitch. Spit?h.'"''- 

In this case we would write P=4,P'=.7854", 5= J". 
i-"~s, or one inch divided by the number of teeth to 
an inch, gives distance on diameter of pitch circle 
occupied by one tooth. The addendum or face of 
tooth is the same distance as s. 

1 _ 



=P, or one inch divided by the distance occupied 



by one tooth equals number of teeth to one inch. 

^■p=t, or 1.57 divided by the diametral pitch gives ^^^J^^^^^'p^^^jP^j; 
thickness of tooth at pitch line. Thus, thickness of ^"^ ^H "Jhick- 

^ llcSS OI X OOLiX 

teeth along the pitch line for 4 diametral pitch is .392". ^.^f"^ Pi^^h 
p = D', or number of teeth in a gear divided by the Number* of 
diametral pitch equals diameter of the pitch circle. an^uie^Diafn- 
Thus for a wheel, GO teeth, 12 P, the diameter oi'i^^fthJmal'^ 
pitch circle will be 5 inches. 'q]%^J;^ ^^^^^ 

-p- =D, or add 2 to the number of teeth in a wheelN umber of 

'P(_»f»|-}j ins, wheel 

and divide the sum by the diametral pitch, and the and the Diame- 

^ tral Pitch to 

find the Whole 
Piameter. 



18 BROWN & SHARPE MFG. CO. 

quotient will be the whole diameter of the gear or the 
diameter of the addendum circle. Thus, for 60 teeth, 
12 P, the diameter of gear blank will be 5^^ inches. 

D'^Pj or number of teeth divided by diameter of 
pitch circle in inches, gives the diametral pitch or 
number of teeth to one inch. Thus, in a wheel, 24 
teeth, 3 inches pitch diameter, the diametral pitch is 8. 
— i)-=P, or add 2 to the number of teeth; divide the 
sum by the whole diameter of gear, and the quotient 
will be the diametral pitch. Thus, for a wheel 3//' 
diameter, 14 teeth, the diametral pitch is 5. 

P D'=:N, or diameter of pitch circle, multiplied by 
diametral pitch equals number of teeth in the gear. 
Thus, in a gear, 5 pitch, 8" pitch diameter, the number 
of teeth is 40. 

•^x-z ' = ®j ^^ divide the whole diameter of a spur gear by 
the number of teeth plus two, and the quotient will be the 
addendum, or a diameter pitch. 

A Diameter Jn future, when we speak of a diameter pitch, we 
shall mean the addendum distance or s. If we speak 
of so many diameter pitches, we shall mean so many 

The Diame- times s, (-jj = s). When we say the diametral pitch we 

tralPitcli. » ^P >> .^ J^ 

shall mean the number of teeth to one inch of diameter 
of pitch circle, or P, (~=^Y). 
ametrai^ PiSh When the circular pitch is given, to find the corre- 
PitS ^^^^^^^'^ sponding diametral pitch, divide 3.1416 by the circular 
pitch. Thus 1.57 P is the diametral pitch correspond- 
ing to 2-inch circular pitch, (— y,i-^=P). 
Example. What diametral pitch corresponds to J" circular 

pitch ? Eemembering that to divide by a fraction we 
multiply by the denominator and divide by the numer- 
ator, we obtain 6.28 as the quotient of 3.1416 divided by 
\ . 6.28 P, then, is the diametral pitch corresponding 
to J circular pitch. This means that in a gear of ^ 
inch circular pitch there are six and twenty-eight one 
hundredths teeth to every inch in the diameter of the 
pitch circle. In the table of tooth parts the diametral 
pitches corresponding to circular pitches are carried 
out to four places of decimals, but in practice two 
places of decimals are enough. 



PROVIDENCE, E. I. 1° 

When two gears are-in mesh, so that their pitch 
circles just touch, the distance between their axes or 
centers is equal to the sum of the radii of the two 
gears. The number of the cUameier pitches between 
centers is equal to half the sum of number of teeth in 
both gears. This principle is the same as given in 
Chapter II., page 6, but when the diametral pitch and^gu^ejo find 
numbers of teeth in two gears are given, add together tween centers. 
the numbers of teeth in the two wheels and divide half 
the sum by the diametral pitch. The quotient is the 
center distance. 

A gear of 20 teeth, 4 P, meshes with a gear of 50 Example, 
teeth: what is the distance between their axes or 
centers ? Adding 50 to 20 and dividing half the sum 
by 4, we obtain 8f " as the center distance. 

The term diametral pitch is also applied to a rack. 
Thus, a rack 3 P, means a rack that will mesh with a 
gear of 3 diametral pitch. 

It will be seen that if the expression for a diameter -j^?J^*^^<^^^} 
pitch has any number except 1 for a numerator, we^^tch. 
cannot express the diametral pitch by naming the 
denominator only. Thus, if the addendum or a diam- 
eter pitch is f ^, the diametral pitch will be 2^, because 
1 divided by y^ equals 2^. 



20 BKOWN & SHAEPE MFS. CO. 



CHAPTER VI. 

SIMLE-CDRYE GEARS HAYINa LESS THAH 30 TEETH— GEARS ABD 
RACKS TO fflESH WITH GEARS HAYING LESS THAH 30 TEETH. 



Construction, jji Yig. 10, the construction of the rack is the same 
as the construction of the rack in Chapter IV. The 
gear in Fig. 10 is drawn from base circle out to adden- 
dum circle, by the same method as the gear in Chapter 
III., but the spaces inside of base circle are drawn as 
follows : 
Gfars''in%ow ^^ gears, 12 and 13 teeth, the sides of spaces 
Teeui^^^^ °^ inside of base circle are parallel for a distance not 
more than -J of a diameter pitch, or J s ; gears 14^ 
15 and 16 teeth not more than ^ s; 17 to 20 teeth, 
not more than ^ s. In gears with more than 20 teeth 
the parallel construction is omitted. 
Construction Then, witli One leff of dividers in pitch circle in 

of Fig. 10 con- ° ^ 

tinned. center of next tooth, e, and other leg just touching 

one of the parallel lines at b, continue the tooth side 
into c, until it will touch a fillet arc, whose radius is 
•J- the width of space -at the addendum circle. The 
part, 5' c', is an arc from center of tooth g, etc. The 
flanks of teeth or spaces in gear. Fig. 11, are made the 
same as those in Fig. 10. 

This rule is merely conventional or not founded 
upon any principle other than the judgment of the de- 
signer, to effect the object to have spaces as wide as 
practicable, just below or inside of base circle, and 
then strengthen flank with as large a fillet as will clear 
addenda of any gear. If flanks in any gear will clear 
addenda of a rack, they will clear addenda of any 

Internal Gear, other gear, except internal gears. An internal gear is 
one having teeth upon the inner side of a rim or ring. 
Now, it will be seen that the gear, Fig. 10, has teeth 



PROVIDENCE, E. I. 



21 




22 BEOWN & SHAEPE MFG. CO. 

too much rounded at the points or at the addendum 
circle. In gears of pitch coarser than 10 to inch (10 
Addfn^Sot -'^)' ^^^ having less than 30 teeth, this rounding 
Teeth. becomcs objectionable. This rounding occurs, because 

in these gears arcs of circles depart too far from the 
true involute curve, being so much that points of 
teeth get no bearing on flanks of teeth in other wheels. 
In gear, Fig. 11, the teeth outside of base circle are 
made as nearly true involute as a workman will be able 
to get without special machinery. This is accomplished 
tior^to^Tmeinl ^^ f ollows : draw three or four tangents to the base 
volute. circle, i i\ j j', h k', 1 1\ letting the points of tangency 

on base circle i',j\ 7c\ I' be about \ or ^ the circular pitch 
apart ; the first point, ^', being distant from ^, equal to 
\ the radius of pitch circle. With dividers set to ^ 
the radius of pitch circle, placing one leg in i', draw 
the arc, a' i j; with one leg in j', and radius j' j, 
draw^ k; with one leg in k', and radius k' k draw k I. 
Should the addendum circle be outside of Z, the tooth 
side can be completed with the last radius, V I. The 
arcs, a' i j^ j k and k I, together form a very close 
approximation to a true involute from the base circle, 
i' j' k' V. The exact involute for gear teeth is the 
curve made by the end of a band when unwound from 
a cylinder of the same diameter as base circle. 

The foregoing operation of drawing tooth sides, 
although tedious in description, is very easy of practical 
application. 
Rounding of It will also be seen that the addenda of rack teeth 

Addenda of 

Rack. in J^ig. 10, interfere with the gear-teeth flanks, as at 

m n/ to avoid this interference, the teeth of rack, Fig. 
11, are rounded at points or addenda. 

It is also necessary to round off the points of invo- 
lute teeth in high numbered gears, when they are to 
interchange with low-numbered gears. In interchange- 
able sets of gears the lowest-numbered pinion is usual- 
Tempietsly 12. Just how much to round off is best learnt by 

necessary for '' 

Rounding off makinsf templets of a few teeth out of thin metal or 
Points of teeth. n, n n ,n j i i. 

cardboard, lor the gear and rack, or, two gears re- 
quired, and fitting addenda of teeth to clear flanks. 
However accurate we may make a diagram, it is quite 



PROVIDENCE, R. I. 



23 



8INQLE CURVE GEAR, 2 P., 12 TEETH. 
IN MESH WITH RACK. 
P=2 
N =12 
P'= 1.57* 
t = .7854' 
S = .500" 
D = 1.000' 
S+f= .5785' 
D'+/ = 1.078' 
D'=6.- 
D = 7.' 



JPiS.ll 



24 



BROWN & SHARPE MFG. CO, 



as well to make templets in order to shape cutters 
accurately. 

A set of cutters for interchangeable gears will give 

good results in finer pitches, made to Fig. 6, in Chapter 

III., for 30 teeth and over, and to Fig. 10, for less 

than 30 teeth, arranged upon the following : 

a "^slf ^or cSt- -^^^^ cutting 12 and 13 teeth, make cutter to diagram 

ters. of 14 teeth. 

For 14 to 16 teeth, diagram of 16 teeth. 



u 17 


" 20 


a 




" 18 


" 21 


" 25 


" 




« 22 


« 26 


" 34 


u 




" 28 


« 35 


" 54 


a 




" 38 


" 55 


"134 


it 




" 55 


" 135 


" rack. 


ii 




"100 



Cut a rack with cutter made to diagram for 100 
teeth. 

For gears, 10 P and coarser, it is better to make 
cutters to corrected diagrams, as in Fig. 11. When 
corrected diagrams are made, as in Fig. 11, take the 
following : 

For 12 and 13 teeth, diagram of 12 teeth. 



" 14 


to 16 






u 14 u 


a 17 


" 20 






u 17 a 


" 21 


" 25 






u 21 « 


" 26 


" 34 






" 26 " 


" 35 


" 54 






" 35 " 


" 55 


" 134 






" 55 " 


" 135 


" rack. 






"135 " 



Templets for large gears must be fiited to run with 
12 teeth, etc. 

We obtain the form for involute cutters by special 
machinery. 



PROVIDENCE, E. I. 25 



CHAPTER VIL 
DOUBLE-CDRYE TEETH— GEAR, 15 TEETH— RACK. 



of_Fig. 12. 



In double-curve teeth the formation of tooth sides ^^^-"^^"^l®" 

cui've Tooth 

changes at the pitch Hne. In all gears the part of ^^^^s are con- 
teeth outside of pitch line is convex ; in some gears 
the sides of teeth inside pitch line are convex ; in some, 
radial ; in others, concave. Convex faces and concave 
flanks are most familiar to mechanics. In interchange- 
able sets of gears, one gear in each set, or of each 
pitch, has radial flanks. In the best practice, this gear 
has fifteen teeth. Gears with more than fifteen teeth, 
have concave flanks; gears with less than fifteen teeth, 
have convex flanks. Fifteen teeth is called the Base 
of this system. 

We will first draw a gear of fifteen teeth. This ^^ Construction 
fifteen-tooth construction enters into gears of any 
number of teeth and also into racks. Let the gear be 
3 P. Having obtained data, we proceed as follows : 

1. Draw pitch cu'cle and j)oint it off into parts equal 
to one-thn-tieth of the circumference, or equal to thick- 
ness of tooth =^. 

2. From the center, through one of these points, as 
at T, Fig. 12, draw line OTA. Draw addendum and 
whole-depth cii'cles. 

3. About this point, T, with same radius as 15-tooth 
pitch circle, describe arcs A K and O k. For any other 
double-curve gear of 3 P., the radius of arcs, A K and 
O k^ will be the same as in this 15-tooth gear =2^". 
In a 15-tooth gear, the arc, O ^, passes through the 
center O, but for a gear having any other number of 
teeth, this construction arc does not pass through 
center of gear. Of course, the 15-tooth radius of arcs, 
A K and O h, is always taken from the pitch we are 
working with. 



26 



BKOWN & SHAKPE MFG. CO. 



—T8 



A^-^ 



G'EAR.S' R.,15 TEETH. 

"P*-3 

N-15 

p/==1,0'472''" 
f =^. ;5236''- 
S=- .3333- 
D'"= .6666' 
S^f^ ;3857" 
D"*/= .7190' 
b'"^ 5.0000' 
D ^5,.6666'' 



_^DDENDUvrc^^.^^^ 




-viHOLTDE PT H~c7RcrE7^ 



v> 



JBT'ig. 13. 

DOUBLE CURVE GEAR. 



"^V *'!!; PEOVIDENCE, R. I. 27 

4. Upon these ai'c^on opposite sides of lines OTA, 
lay off tooth thickness, A K and O k, and draw line 
K T ^•. 

5. Perpendicular to K T ^, draw line of pressure, 
L T P ; also through O and A, draw lines A E and O r, 
perpendicular to K T ^. The line of pressure is at 
an angle of 78° with the radius of gear. 

6. From O, draw a line O R to intersection of A R 
with K T A;. Through point c, where O R intersects 
L P, describe a circle about the center, O. In this 
circle one leg of dividers is placed to describe tooth 
faces 

7. The radius, c d, of arc of tooth faces is the 
straight distance from c to tooth-thickness point, h, 
on the other side of radius, O T. With this radius, c h, 
describe both sides of tooth faces. 

8. Draw flanks of all teeth radial, as O 6 and O f 
The base gear^ 15 teeth only, has radial flanks. 

9. With radius equal to one sixth of the widest part 
of space, as g h, draw fillets at bottom of teeth. 

The foregoing is a close approximation to epicy- . Approxima- 
cloidal teeth. To get exact teeth, make two IS-toothcioidai Teeth. 
gears of thin metal. Make addenda long enough to 
come to a point, as at n and q. Make radial flanks, as 
at m and p, deep enough to clear addenda when gears 
are in mesh. First finish the flanks, then fit the long 
addenda to the flanks when gears are in mesh. 

When these two templet gears are alike, the centers standard 

, -1 . -1 , -i . - , Templets. 

are the right distance apart and the teeth interlock 
without backlash, they are exact. One of these tem- 
plet gears can now be used to test any other templet 
gear of the same pitch. 

Gears and racks will be right when they run cor- 
rectly with one of these 15-tooth templet gears. Five 
or six teeth are enough to make in a gear templet. 

Double-curve Rack. — Let us draw a rack 3 P. ^ ^o^^i?-^^7® 

. . A Kack, Fig. 13. 

Having obtained data of teeth we proceed as follows : 

1. Draw pitch line and point it off in parts equal 
to one-half the circular pitch. Draw addendum and 
whole-depth lines. 

2. Through one of the points, as at T, Fig. 13, draw 
line OTA perpendicular to pitch line of rack. 



28 



BROWN & SHARPE MFG. CO. 




Wi^. 13 

DOUBLE CURVE RACK.. 



PEOYIDENCE, R. I. 



29 



3. About T make precisely the same construction as 
was made about T in Fig. 12. That is, with radius of 
] 5-tooth pitch cu'cle and center T draw arcs O k and 
A K ; make O k and A K equal to tooth thickness ; 
draw K T X; y draw O r, A R, and line of pressure, each 
perpendicular to K T ^. 

4. Through R and r, draw lines parallel to O A. 
Through intersections c and c' of these lines, with 
pressm-e line L P, draw lines parallel to pitch line. 

5. In these last lines place leg of dividers, and draw 
faces and flanks of teeth as in sketch. 

6. The radius c' d' of rack-tooth faces is the same 
length as radius c ^ of rack-tooth flanks, and is the 
straight distance from c to tooth-thickness point h on 
opposite side of line O A. 

7. The radius for fillet at bottom of rack teeth is 
equal to \ of the widest part of tooth space. This 
radius can be varied to suit the judgment of the 
designer, so long as a fillet does not interfere with 
teeth of engaging gear. 




li^is- 14 



Racks of the same pitch, to mesh with interchange- 
able gears, should be alike when placed side by side, 
and fit each other when placed together as in Fig. 14. 

In Fig. 13, a few teeth of a 1 5-tooth wheel are shown 
in mesh with the rack. 



30 ' BROWN & SHARPE MFG. CO. 



CHAPTER VIII. 

DODBLE-CURVE GEARS, HAVIHa MORE AMD LESS THAN 
15 TEETH— AMULAR GEARS. 



of Mgf ^i?''*'^'^ ^^^ ^^ ^^^ *^^ gears, 12 and 24 teetli, 4 P, in 
mesh. In Fig. 15 the const.ruction lines of the lower 
or 24-tooth gear are full. The upper or 12-tooth gear 
construction lines are dotted. The line of pressure, 
L P, and the line K T ^ answer for both gears. The 
arcs A K and O k are described about T. The radius 
of these arcs is the radius of pitch circle of a gear 15 
teeth 4 pitch. The length of arcs A K and O >^ is the 
tooth thickness for 4 P. The line K T ^ is obtained 
the same as in Chapter VII. for all double-curve gears, 
the distances only varying as the pitch. Having drawn 
the pitch circles, the line K T ^, and, perpendicular to 
K T ^, the lines A K, O r and the line of pressure 
L T P, we proceed with the 24-tooth gear as follows : 

1. From center C, through r, draw line intersecting 
line of pressure in m. Also draw line from center C 
to R, crossing the line of pressure L P at c. 

2. Through m describe circle concentric with pitch 
circle about C. This is the circle in which to place 
one leg of dividers to describe flanks of teeth. 

3. The rad.ius, m n, of flanks is the straight distance 
from m to the first tooth-thickness point on other side 
of line of centers, C C', at v. The arc is continued to 
71, to show how constructed. This method of obtain- 
ing radius of double-curve tooth flanks applies to all 
gears having more than fifteen teeth. 

4. The construction of tooth faces is similar to 15- 
tooth wheel in Chapter YII. That is : Draw a circle 
through c concentric to pitch circle ; in this circle 
place one leg of dividers to draw tooth faces, the 
radius of tooth faces being c h. 



PEO^^DENCE, K. I. 



31 




PINION 


,12 TEETH^ 


GEAR 24- TEETH, .4 P 


P=4 


N = 


12 and 24, 


P'= 


.7854' 


t = 


.392r 


8 = 


.2500' 


D'= 


.5000' 


st/ = 


.2893' 


D'+/ = 


.5393' 






DOUBLE CURVE GEARS IN MESH. 



32 BROWN & SHAEPE MFG. CO. 

of FirS'^'con^ ^' ^^® ^^^^^^ ^^ ^^^®*^ ^* ^'^O*^ O^ *®^*^ is ^q^al to 

tinued. one-sixth the width of space at addendum circle. 

Flanks for 12, ^hc construclloiis for flanks of 12, 13 and 14 

13 and 14 Teeth, teeth are similar to each other and as follows : 

1. Through center, C, draw line from K, intersecting 
line of pressure in u. Through u draw circle about 
C In this circle one leg of dividers is placed for 
drawing flanks. 

2. The radius of flanks is the distance from u to 
the first tooth- thickness point, e, on the same side of 
C T C. This gives convex flanks. The arc is con- 
tinued to V, to show construction. 

3. This arc for flanks is continued in or toward the 
center, only about one- sixth of the working depth (or 
Js.); the lower part of flank is similar to flanks of 
gear in Chapter VI. 

4. The faces are similar to those in 15- tooth gear, 
Chapter VII., and to the 24-tooth gear in the fore- 
going, the radius being iv y ; the arc is continued to x^ 
to show construction. 

Annular Gears. Annular Gears. Gears with teeth inside of a rim 
or ring are called Annular or Internal Gears. The 
construction of tooth outlines is similar to the fore- 
going, but the spaces of a spur external gear become 
the teeth of an annular gear. 

Prof. MacCord has shown that in the system just 
described, the pinion meshing with an annular gear, 
must differ from it by at least fifteen teeth. Thus, 
a gear of 24 teeth cannot work Avith an annular gear 
of 36 teeth, but it will work with annular gears of 39 
teeth and more. An annular gear differing from its 
mate by less than 15 teeth can be made. This will be 
shown in Part II. 

Annular-gear patterns require more clearance for 
moulding than external or s]3ur gears. 
Pinions. In speaking of different-sized gears, the smallest 

ones are often called " pinions." 

The angle of pressure in all gears except involute, 
constantly changes. 78° is the pressure angle in 
double-curve, or epicycloidal gears for an instant 
only ; in our example, it is 78° when one side of a 



PROVIDENCE, R. I. 



33 



tooth readies the line of centers, and the pressm-e 
against teeth is applied in the direction of the arrows. 

The pressure angle of involute gears does not 
change. An explanation of the term angle of pressure 
is given in Part II. 

We obtain the forms for epicycloidal gear cutters 
by means of a machine called the Odontom Engine. 
This machine will cut original gears with theoretical 
accuracy. 

It has been thousfht best to make 24 efear cutters 24 Double 

° ° curve Gea 

for each pitch. This enables us to fill any require- cu tters fo 

^ ^ J M each Pitch. 

ment of gear-cutting very closely, as the range covered 
by any one cutter is so small that it is exceedingly near 
to the exact shape of all gears so covered. 

Of course, a cutter can be exactly/ right for only one 
gear. Special cutters can be made, if desired. 





1 PITCH TOOTH CURVES 

from the 
ODONTOM ENGINE. 



34 BBOWN & SHABPE MFG. CO. 



CHAPTER IX. 
BEYEL-GEAR BLABKS. 



The pitch of bevel gears is always figured at the 
largest pitch diameter. 

Most bevel gears connect shafts that are at right 

angles with each other, and unless stated otherwise, 

we always understand they are so wanted. 

Diagram/^Fig. The directions given in connection with Fig. 16 apply to 

8 1 r u°ct?o n^of n^^^^ ^^^^ ^^^^ ^^ right angles. Having decided upon the 

Blanks!" ^^^'" pitch and the numbers of teeth. 

1. Draw center lines of shafts, A O B and COD, 
at angle required. 

2. Parallel to A O B, draw lines a b and c d, each 
distant from A O B, equal to half the largest pitch 
diameter of one gear. For 24 teeth, 4 pitch, this half 
largest pitch diameter is 3". 

3. Parallel to C O D, draw lines e/and g A, distant 
from COD, equal to half the largest pitch diameter 
of other gear. For gear, 12 teeth, 4 pitch, this half 
largest pitch diameter is 1^". 

4. At intersections of these four lines, draw lines 
O i, Oj, O k, and 1; these lines give the size and 
shape of pitch cones. We call them " Cone Pitch 
Lines." 

5. Perpendicular to cone-pitch lines and through 
intersection of lines a b, c d, e f, g h, draw lines m n, 
op, qr. We have also drawn u v to show that another 
gear can be drawn from same diagram. Four gears, two of 
each size, can be drawn from same diagram. 

6. Upon lines m n, op, q r, the addenda and depth 
of teeth are laid off, these lines being passed through 
the largest pitch diameter of gears. Lay off the adden- 



PROVIDENCE, K. I. 



35 





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ITio. IG 







36 BKOWN & SHAEPE MFG. CO. 

dum, it being in these gears j^'\ This gives distance 
m n, op, q r and u v equal to the working depth of 
teeth, in these gears ^". The addendum, of course, is 
measured perpendicularly from cone pitch lines as at k r. 

7. Draw lines O m, O n, O o, O p, O q, O r. These 
lines give the height of teeth above cone-pitch lines 
and the working depth of teeth. The teeth become 
smaller as they approach O and would vanish entirely 
at O. It is quite as well never to have length of teeth, 
or face, m m' longer than one-third the distance m O, 
nor more than ^\ times the circular pitch. 

8. Having decided upon the length of face, draw 
limiting lines m' n perpendicular to i O, q r' perpen- 
dicular to k O, and so on. 

We have now the outline of section of gears through 

their axes. The distance m r y^ the whole diameter of 

pinion. The distance q o i^ the whole diameter of 

gear. In practice these diameters are obtained by 

The Whole measuring the drawing. The diameter of pinion is 

Bevel .Gear 3.45" and of gear 6.22". We also find angles by meas- 

eraiiy ohtained ui'ing drawing with a protractor. In the absence of a 

by Measuring o o j. 

Drawings. protractor templates can be cut to drawing. The 
angle formed by line m m' with a 5 is the angle of 
face of pinion, in this pinion 59° 11' or 59|° nearly. The 
lines q q' and g h give us angle of face of gear, for this 
gear 22° 19' or 22J° nearly. The angle formed by m n 
with a h m called the angle of edge of pinion, in our 
sketch 26° 34', or about 26^°. The angle of edge of 
gear, line q r with g h is 63° 26', or about 63^°. In 
turning blanks to these angles we place one arm of 
the protractor or template against end of hub, when 
trying angles of a blank. Some designers give angles 
from the axes of gears, but it is not convenient to try 
blanks in this way. The method we have given also 
comes right for angles as figured in compound rests. 

When axes are at right angles, the sum of angles of 
edge in the two gears equals 90°, and the sums of 
angle of edge and face in each gear are alike. 

The angle of axes remaining the same, all pairs of 
bevel gears of same ratio have the same angle of edge ; 
all pairs of same ratio and of same numbers of teeth 



PROVIDENCE, R. I. 37 

have the same angles of both edges and faces inde- 
pendent of the pitch. Thus, in all pairs of bevel gears 
having one gear twice as large as the other, with axes 
at right angles, the angle of edge of large gear is 63° 
26', and the angle of edge of small gear is 26° 34'. 

In all pahs of bevel gears with axes at right angles, 
one gear having 24 teeth and the other gear having 12 
teeth, the angle of face of large gear is 22° 19', and the 
angle of face of small gear is 59° 11'. 

The following method of obtaining the whole 
diameter of bevel gears is sometimes preferred: 

From h lay off, upon the cone-pitch line, a distance Another 

•^ ' -^ ^ ' method of oh- 

K 10. equal to ten times the workinsf depth of the taming whoie 

Diameter of 

teeth=10D". Now add j'q- of the shortest distance of Blanks. 

to from the line g A, which is the perpendicular dotted 

line %o X, to the outside pitch diameter of gear, and the 

sum will be the whole diameter of gear. In the same 

, manner -^^ of lo y, added to the outside pitch diameter 

of pinion, gives the whole diameter of pinion. 

A somewhat similar construction will do for bevel gears ^Connection of 

o Blanks of Reel 

whose axes are not at risrht anojles. Gears whose 

Axes are not 

In hig. 16 A, the axes are shown at B and D, the at Right Angles 
angle BOD being less than a right angle. 

1. Parallel to B, and at a distance from it equal to the 
radius of the gear, we draw the lines a b and c d. 

2. Parallel to D, and at a distance from it equal to the 
radius of the pinion, we draw the lines e f and g h. 

3. Xow, through the point j at the intersection of c d 
and g h, we draw a line perpendicular to B. This Hne k 
j, limited by a b and c d, represents the largest pitch diameter 
of the gear. 

4. Through j we draw a line perpendicular to D. This 
line j 1, limited by e f and g h, represents the largest pitch 
diameter of the pinion. 

5. Through the point k at the intersection of a b with k 
j, we draw a line to 0, a line from j to 0, and another from 
1, at the intersection j 1 and e f to 0. These hnes k, 
j, O 1, represent the cone pitch line as in Fig. 16. 

6. Perpendicular to the cone pitch lines we draw the 
lines u V, p and q r. Upon these Hnes we lay off the 
addenda and working depth as in the previous figure, and 
then draw lines to the point as before. By a similar con- 
«truction Figs. 16 B and 16 C can be drawn. 



38 



BROWN & SHARPE MFG. CO. 




1GB. 




Fig. 16 C. 



PROVIDENCE, E. I. 



39 




STOCKING CUTTER. 




WORM THREAD TOOL GAUGE. 



.269 



8 PITCH 



BROmiS, SHAEPE MFG CO. 
PROVIDENCE. R.1 



• O 



DEPTH OF GEAR TOOTH GAUGE. 



40 BROWN & SHARPE MFG. CO. 



CHAPTER X. 
BEVEL GEARS— FORM AND SIZE OF TEETH— CDTTIBa TEETH. 



To obtain data for teeth, we need only make drawing 
of section of one-half of each gear. 

1. We first draw center lines A O and B O, Fig. 17, 
and the lines g h and c d, then gear blank lines as in 
Chapter IX. 

in bevei^^ear? ^^ obtain shape of teeth in bevel gears we do not lay 
them off on pitch circles the same as we would in spin* 
gears. A line running from a point on cone-pitch line 
to center line of a bevel gear and perpendicular to the 
cone-pitch line, is the radius for circle apon which to 
draw outlines of teeth at this point. 

2. Thus, A c is the geometrical pitch circle radius 
for large end of teeth, and A' c' the geometrical pitch 
radius for small end of teeth of wheel. To avoid con- 
fusion, we have transferred the distance A' & to the 
line A c". 

3. For the pinion we have the geometrical pitch 
circle radius B c for large end of teeth, and the radius 
B' c' for small end of teeth. We have transferred the 
distance B' c' to the line B c'". 

4. About A draw the arc c n m, and upon it lay off 
spaces equal to the thickness of tooth at pitch line, 
and draw outlines of teeth as in previous chapters. 
That is, for single-curve teeth draw a semicircle upon 
radius Ao and proceed as in Chapter III. For all bevel 
gears cut with a rotary disk-cutter (a common gear- 
cutter), single-curve teeth are preferable. Double- 
curve teeth can be drawn from instructions in Chapters 
VII. and VIII. We now have the shape of teeth at 
large end of gear. Repeat this operation with radius 
B c about B, and we have form of teeth at large end 
of pinion. 



PKOTIDENCE, K. lo 



41 




PINION 18 TEETH. 
GEAR, 24- TEETH.5 P. 
P =5. 

NHS and 24 
F'= .628- 
t = .314" 
S = .200" 
D"= .400' 
S+f= .231' 
D'= + / = .431' 



t' = .209' 
= .133" 
D"= .266' 
s'+f =.165- 
D"+/ =.298' 



BEVEL GEARS., FORM AND SIZE OF TEETH. 



42 BROWN & SHARPE MFG. CO. 

5. Upon arc of radius A' c' we get shape of teeth at 
small end of gear, and upon arc of radius B' c' we get 
shape of teeth at small end of pinion. 
Sizes of teeth 6. The sizes of tooth parts at small end can be taken 

at small end ^ 

by diagram, directly from diagram, or they can be calculated. By 
tmeasuring the distance^' c' and c' o',we obtain adden- 
dum and working depth of teeth at inside of the gears. 
The thickness of teeth at inside is given at m n' by 
lines m n running to A, the distance rt% n being the 
thickness of tooth at outside. We designate tooth 
parts at inside by adding one more accent to the 
corresponding designation for tooth parts at outside, 
which are the same as those for spur gears. The tooth 
parts inside are denoted thus: t\ s', D'", 5' + /, T>"' ■\-f. 
All elements of the teeth run to the point O, where 
axes of gears meet. The sizes of tooth parts at small 
end can be calculated as follows : (These sizes bear the 
same ratio to the corresponding sizes at outside of 
4gears that the distance O e' does to O c.) 
Sizes of teeth Dividing the distance O c', which in our example is 

calculation. ^ 2", by O c, which in this case is 3", we obtain J or .666 as 
the ratio. Multiplying the outside sizes by .^^^, we ob- 
tain the corresponding inside sizes (see Fig. 17). Thus, 
the thickness of teeth at outside being .314, we take f of 
.314" and obtain .209" as the thickness of teeth inside. 
Cutting Bev- When cutting bevel gears with rotary cutters the 

Kotary Cutters, angle of cutter-head is set the same as angle of 
working depth ; thus : To cut the gear we have the 
cutter travel in the direction of line O p. The angle 
A O ^ is called the " Cutting Angle," being measured 
from the axis of gear. In the method here adopted 
the angle of face of pinion is the same as cutting angle 
of gear, and face angle of gear is the cutting angle of 
pinion ; so that /*, or clearance at bottom of spaces, is 
the same at inside of gear as f at the outside of gear. 
Side Angle The cutter-head in some gear-cutting engines can 
' be set at an angle sidewise as well as toward the 
work spindle. 

In such engines, for cutting bevel gears, take cutter 
of right curve for teeth about one-third the length of 
tooth from large end ; this gives teeth with sides not 



PROVIDENCE, E. I. 43 

enough cui'ved at small end. In pinions it is some- 
times necessary to file teeth at small ends ; the cutter 
should, of coui'se, be thin enough to go through space 
at small end. In these engines the spaces at large end 
of teeth are made wide enough by setting the cutter- 
head sidewise, two settings and two cuts being applied 
to each gear ; but after the first gear the setting is 
changed once only for each gear. In most engines Different Cut- 
there is no provision for side angle, and the width of chines without 
spaces is obtained by tui-ning the work spindle and 
setting cutter out of center. When the cutting angle 
of gears is greater than 45 '^ the teeth cut by the two 
engines are about alike ; but when the cutting angle is 
less than 45 ', the same cutter will make the adden- 
dum of teeth more rounding in the cutting engine with 
no side angle than it will in the cutting engine with 
side angle. In such cases a corresponding allowance 
should be made in the shaping of cutters. In ordering jyiYiVin^^li^ 
bevel-gear cutters it should be stated which kind of ciiines can be 
engme the cutters are to be used in. The Universal ways. 
Milling Machine can be used for either side angle or 
rotation of work spindle. 

We can plane bevel gears up to 16" diameter, theo- We can plan© 
retically exact, each gear being an original one. Gears. 

We have recently added to our Gear Cutting Department 
a Gear Planer, which enables us to plane Spur or Bevel 
gears up to 48 inches diameter and of any pitch or form of 
teeth desired. 




44 BKOWN & SHAEPE MFG. CO. 



CHAPTER XI. 
WORM WHEELS— SIZING BLANKS OF 32 TEETH AND OVER. 



Worm. ^ WORM is a screw made to mesh with the teeth of 

a wheel called a worm-wheel. As implied at the end of 
Chapter IV., a section of a worm through its axis is, in 
outline, the same as a rack of corresponding pitch. 
This outline can be made either to mesh with single or 
double curve gear teeth ; but worms are usually made 
for single curve, because, the sides of involute rack 
teeth being straight (see Chapter IV.), the tool for 
cutting worm-thread is more easily made. The thread- 
tool is not usually rounded for giving fillets at bottom 
of worm-thread. 

The rules for circular pitch apply in the size of tooth 
parts and diameter of pitch-circle of worm-wheel. 

Pitch of Worm. The pitch of a worm or screw is usually given in a 
way different from the pitch of a gear, viz. : in number 
of threads to one inch of the length of the worm or 
screw. Thus, if we say a worm is 2 pitch we mean 2 
threads to the inch, or the worm makes two turns to 
advance the thread one inch. But a worm may be 
double-threaded, triple-threaded, and so on. 

To avoid misunderstanding it is better always to 

Worn5Tiirea(f. Call the advance of the worm thread the lead. Thus, a 
worm-thread that advances one inch in one turn we 
call one -inch lead in one turn. A single-thread worm 
4 to 1" is J" lead. We apply the term pitch to the actual 
distance between the threads or teeth, as in previous 
chapters. In single-thread worms the lead and the 
pitch are alike. If we have to make a worm and wheel so 
many threads to one inch, we first divide 1" by the num- 
ber of threads to one inch, and the quotient gives us 
the circidar pitch. Hence, the wheel in Fig. 19 is \" 

Linear Pitcii. circular pitch. The term linear pitch expresses ex- 



PROVIDENCE, E. I. 



45 




Fig. 18.-W0RM AND WORM-WHEEL 

The thread of Wopm is left-handed ; Worm is single-threaded. 



46 



BROWN & SHAKPE MFG. CO. 




PROVIDENCE, R. I. 47 

actly what is meant by circular pitch. Linear pitch 
has the advantage of being an exact use of language 
when applied to worms and racks. The number of 
thi-eads to one inch lineal', is the reciprocal of the linear 
pitch. 

Multiply 3.1416 by the number of threads to one 
inch, and the product will be the diametral pitch of the 
worm-wheel. Thus, we would say of a double-thread 
worm advancing 1" in IJ turns that: 

Lead=f" or .75". Linear pitch or P'=#" or .375". Drawing of 

* ^ ° Wormand 

Diametral pitch or P = 8. 377. See table of tooth parts. Worm-wiieei. 
To make di'awing of worm and wheel we obtain 
data as in circular pitch. 

1. Draw center line A O and upon it space off the 
distance a h equal to the diameter of pitch-circle. 

2. On each side of these two points lay off the dis- 
tance s, or the usual addendum =^ , as 5 c and h d. 

3. From c lay off the distance c O equal to the 
radius of the worm. The diameter of a worm is gen- 
erally four or five times the circular pitch. 

4. Lay off the distances c g and d e each equal to/*, 
or the usual clearance at bottom of tooth space. 

5. Through c and e di^aAV circles about O. These 
represent the whole diameter of worm and the diam- 
eter at bottom of worm-thread. 

6. Draw h O and i O at an angle of 30° to 45° with 
A O. These lines give width of face of worm-wheel. 

7. Through g and d draw arcs about O, ending in 
h O and i O. 

This operation repeated at a completes the outline 
of worm-wheel. For 32 teeth and more, the addendum 
diameter, or D, should be taken at the throat or 
smallest diameter of wheel, as in Fig. 19. Measure 
sketch for tchole diameter of wheel-blank. 

The foregoing instructions and sketch are for cases t e e t h o f 
where the teeth of the wheels are finished with a hob. ished with Hob. 

A HOB is shown in Fig. . 20, being a steel piece Hob. 
threaded with the same tool that threads the worm, 
then grooved to make teeth for cutting, and hardened. 

The whole diameter of hob should be 2/, or twice proportionsof 
the clearance larger than the worm. The outer cor- ^^^' 



48 BROWN & SHARPE MFG. CO. 

ners of hob-tln-ead can be rounded down as far as the 
clearance distance. The width at top of the hob-thread 
before rounding should be .31 of the linear, or circular 
pitch=.31P'. The whole depth of thi-ead should be 
the ordinary working depth plus the clearance = 
D"+/. The diameter at bottom of hob-thread should be 
2/ larger than the diameter at bottom of worm-thread. 
For thread-tool and worm-thread see end of Chapter TV, 
The thickness of cutter for grooving small hobs, say less than 
two inches diameter, can be about i the width of thread at 
top plus i"=^.^^'-\-V'. The width of lands at the bottom 




Fig. 20.-H0B. 



can be about the depth of thread plus i''=D"4-2/-f i''. The 
grooves are usually cut with a round edge cutter, the parallel 
part of cutter just reaching the bottom of thread, making 
the half-round bottom of grooves below the bottom of 
thread. In small hobs, the teeth are often not relieved 
between the grooves. In large hobs or those more than 
three inches diameter, the teeth may be cut with radial 
faces, cutting the space wider at the outer part so as to leave 
the faces and backs of teeth about parallel, and the teeth 
should be relieved. This can be done in our Universal 
MilHng Machine. A common way in hobs two to three 
inches in diameter, is to relieve with a file. 



PROVIDENCE R. I. 49 

The teeth of the wheel are first cut as nearly to 
the finished form as practicable ; the hob and worm- 
wheel are mounted upon shafts and hob placed in mesh 
as in Fiof. 18. The hob is now made to rotate, and is^^^ow to use 

'^ ' tne Hob. 

dropped deeper into the wheel at each revolution of the 
wheel until teeth are finished. The hob generally 
di'ives the worm-wheel during this operation. The 
Universal Milling Machine is very convenient for doing Universal 
this work, and with it the distance between axes of chine used in 
worm and wheel can be readily noted. Where a great 
many wheels are manufactured special machines have 
been made for driving wheels independent of hob. The why a wheel 
object of bobbing a wheel is to get more bearing sur- 
face of the teeth upon worm-thread. The worm-wheels, 
Figs. 18 and 26, were hobbed. By bobbing we pro- 
duce outline of teeth something like the thread of a nut. 

If we make the diameter of a worm-wheel blank, that Worm- wheel 

Blanks with 

IS to have less than 30 teeth, by the common rules Less than 3o 

Teeth 

for sizing blanks, and finish the teeth with a hob, we 
shall find the flanks of teeth near the bottom to be U7i- 
dercut or hollowinef. This is caused by the interf er- ^ interference 

° *' of Thread and 

ence spoken of in Chapter YI. Thirty teeth was there Flank. 
given as a limit, which will be right when teeth are 
made to circle arcs. With pressure angle 75J^°, and 
rack-teeth with usual addendum, this interference of 
rack-teeth with flanks of gear-teeth commences at 31 
teeth {^1-Yo geometrically), and interferes with nearly 
the whole flank in wheel of 12 teeth. 

In Fig 21 the blank for worm-wheel of 12 teeth was Fig. 21. 
sized by the same rule as given for Fig. 19. The wheel 
and worm are sectioned to show shape of teeth at the 
mid-plane of wheel. The flanks of teeth are undercut 
by the hob. The worm-thread does not have a good 
bearing on flanks inside of A, the bearing being that of 
a corner against a surface. 

In Fig 22 the blank for wheel was sized so that pitch- ^^s. 22. 
circle comes midway between outermost part of teeth 
and innermost point obtained by worm thread. 



50 



BKOWN & SHARPE MFG. CO. 



^NfC^'fCi., 




E^ig. Jil. 



PKO^^DENCE, E. I. 



51 



:H ,,CIR 




Fig. SS. 



52 BROWN & SHAEPE MFG. CO. 

This rule for sizing worm-wheel blanks has been in 
use to some extent. The hob has cut away flanks of 
teeth still more than in Fig. 21. The pitch-circle in 
Fig. 22 is the same diameter as the pitch-circle in Fig. 
21. The same hob was used for both wheels. The 
flanks in this wheel are so much undercut as to mate- 
rially lessen the bearing surface of teeth and worm- 
thread. 
Interference In Chapter VI. the interference of teeth in high- 
numbered gears and racks with flanks of 12 teeth was 
remedied by rounding off the addenda. Although it 
would be more systematic to round off the threads of 
a worm, making them, like rack-teeth, to mesh with 
interchangeable gears, yet this has not generally been 
done, because it is easier to make a worm-thread tool 
with straight sides. 

Instead of cutting away the addenda of worm- 
thread, we can avoid the interference with flanks of 
wheels having less than 30 teeth by making wheel 
blanks larger, 
Pig. 23. The flanks of wheel in Fig. 23 are not undercut, be- 

cause the diameter of wheel is so large that there is 
hardly any tooth inside the pitch-circle. The 
pitch-circle in Fig. 23 is the same size as pitch- 
circles in Figs. 21 and 22. This wheel was sized 
Diameter at bv the following rule : MmIUxAy the pitch diameter oi 

Throat to Avoid '^ ° r J s- 

Interference, the wheel by .937, and add to the product four times 
the addendum (4 s) ; the sum will be the diameter for 
the blank at the throat or small part. To get the 
whole diameter, make a sketch with diameter of throat 
to the foregoing rule and measure the sketch. 

It is impractical to hob a wheel of 12 to about 16 or 
18 teeth when blank is sized by this rule, unless the 
wheel is driven by independent mechanism and not by 
the hob. The diameter across the outermost parts of 
teeth, as at A B, is considerably less than the largest 
diameter of wheel before it was hobbed. 

In general it is well to size all blanks, as by page 45 
and Figs. 19 and 21, when the wheels are to be 
hobbed. Of course, if the wheel is to be hobbed the 



PROVIDENCE, R. I. 



53 



9^1^^ i^^^' 




Fig. 23. 



54 BROWN & SHARPE MFG. CO. 

cutter should be thin enough to leave stock for finish- 
ing. The spaces can be cut the full depth, the cutter 
being dropped in. 

To get angle of worm-thread, it is best to apply pro- 
tractor directly to the thread, as computing the 
angle affords but little help. Set gear cutter-head as 
near the angle as can be seen from trial with 
protractor upon thread ; cut a few teeth ; try in worm. 
Generally the cutter-head has to be changed before 
the worm will take the right position. 

When worm-wheels are not hobbed it is better to 
s ^^r wheS^ ^ tuYJi blanks like a spur-wheel. Little is gained by 
having wheels curved to fit worm unless teeth are fin- 
ished with a hob. The teeth can be cut in a straight 
path diagonally across face of blank, to fit angle of 
worm-thread, as in Figs. 24 and 27. 
Wheels for For dividing wheels to gear-cutting engines the 
Machines. blanks are turned like a spur-wheel and a cutter about 
-^" larger diameter than the worm, is dropped in, as 
in Figs. 25 and 28, and the worm-thread is slightly 
rounded at the outer corners. The radius for rounding 
thread can be J the width of thread at the top. 

Some mechanics prefer to m^ke dividing wheels in 
two parts, joined in a plane perpendicular to axis, hob 
teeth ; then turn one part round upon the other, match 
teeth and fasten parts together in the new position, 
and hob again with a view to eliminate errors. 

With an accurate cutting engine we have found 
wheels like Figs. 25 and 28, not hobbed, every way 
satisfactory. Dividing wheels of 2 feet diameter and 
less are generally made without arms, the part between 
hub and rim being a solid web. As to the different 
Figures 26, 27 wheels, Figs. 26, 27 and 28, when worm is in right 
position at the start, the life-time of Fig. 26, under 
heavy and continuous work, will be the longest. 

Fig. 27 can be run in mesh with a gear or a rack as 
well as with a worm when made within the angular limits 
commonly required. Strictly, neither two gears made in this 
way, nor a gear and a rack would be mathematically exact 
as they might bear on the sides of the gear or at the ends of 
the teeth only and not in the middle. A' tl e &tart the con- 



PROVIDENCE, E. I. 



55 




Fig, 24. 



■Worm-wheel with teeth cut in a straight path diagonally across face. 
Worm is double-threaded. 



56 



BEOWN & SHAKPE MFG. CO. 




TATorm and ^Vo^m- Wheel, for Gear-cutting Engine. 



PKOVIDENCE, R. I. 



57 



Fig. kii5. 



Fig. 27, 



IFig. 38. 



58 BROWN & SHARPE MFG. CO. 

tact of teeth in this wheel upon worm-thread is in points 
only: yet such wheels have been many years successfully 
used in elevators. 

Fig. 28 is a neat-looking wheel. In gear cutting 
engines where the workman has occasion to turn the 
work spindle by hand, it is not so rough to take hold 
of as Figs. 26 and 27. The teeth are less liable to in- 
jury than the teeth of Figs. 26 and 27. 

Some designers prefer to take off the outermost part 
of teeth in wheels (Figs. 18 and 26), as shown in these 
two figures, and not leave them sharp, as in Fig. 19. 

We do not know that this serves any purpose except 
a matter of looks. 

In ordering worms and worm wheels the centre distances 
should be given. 

If there can be any limit allowed in the centre distance it 
it should be so stated. 

For instance, the distance from the centre of a worm to the 
centre of a worm wheel might be calculated at 6'' but 
5 31-32'' or 6 1-32'' might answer. 

By stating all the limits that can be allowed, there may be 
a saving in the cost of work because time need not be wasted 
in trying to make the work within narrower limits than 
need be. 



HOBS WITH RELIEVED TEETH. 



We are prepared to make hobs of any size with the teeth 
relieved the same as our gear cutters. The teeth can be 
ground on their faces without • changing their form. The 
hobs are made with a precision screw so that the pitch of 
the thread is accurate before hardening. 



PBOVIDBNOE, B. I. 59 



CHAPTER XII. 

SIZING GEftRS WHEN THE DISTANCE BETWEEN CENTERS AND THE 
RATIOS OF SPEEDS ARE FIXED— GENERAL REMARKS— WIDTH 
OF FACE OF SPUR GEARS— SPEED OF GEAR CDTTERS— TABLE 
OF TOOTH PARTS. 



Let us suppose that we have two shafts 14" apart, 
center to center, and wish to connect them by efears so, center dis- 

' *' o tance and Ratio 

that they will have speed ratio 6 to 1. We add the 6 fi^^^. 
and 1 together, and divide 14" by the sum and get 2" ' 
for a quotient; this 2", multiplied by G, gives us the 
radius of pitch cu'cle of large wheel = 12". In the same 
manner we get 2" as radius of pitch circle of small wheel. 
Doubling the radius of each gear, we obtain 24" and 4" 
as the pitch diameters of the two wheels. The two num- 
bers that form a ratio are called the terms of the ratio. 
We have now the rule for obtaining pitch-circle diame- 
ter of two wheels of a given ratio to connect shafts a 
given distance apart : 

Divide the center distance hy the sum of the terms of ^^"le for du 

^ ^ J ameterof Pitcli 

the ratio; find the product of twice the quotient hy each ^^^'^^^^^ 
term separately, and the two products will he the pitch 
diameters of the tv;o loheels. 

It is well to give special attention to learning the 
rules for sizing blanks and teeth ; these are much 
oftener needed than the method of forming tooth out- 
hnes. 

A blank 1^" diameter is to have 16 teeth: what will 
the pitch be? What will be the diameter of the pitch 
circle? See Chapter Y. 

A good practice will be to compute a table of tooth 
parts. The work can be compared with the tables 
pages 68-71. 



60 BROWN & SHARPE MFG. CO. 

In computing it is well to take n to more than four 
places, 7t to nine places = 3,141592653. ^ to nine 
places = .318309886. 

There is no such thing as pure rolling contact in 
teeth of wheels ; they always rub, and, in time, will 
wear themselves out of shape and may become noisy. 

Bevel gears, when correctly formed, run smoother 
than spur gears of same diameter and pitch, because 
the teeth continue in contact longer than the teeth of 
spur gears. For this reason annular gears run smoother 
than either bevel or spur gears. 

Sometimes gears have to be cut a little deeper than 
designed, in order to run easily on their shafts. If 
any departure is made in ratio of pitch diameters it is 
better to have the driving gear the larger, that is, cut 
the follower smaller. For wheels coarser than eight 
diametral pitch (8 P), it is generally better to cut twice 
around, when accurate work is wanted, also for large 
wheels, as the expansion of parts from heat often causes 
inaccurate work when cut but once around. There is 
not so much trouble from heat in plain or web gears as 
in arm gears. 
Width of Spur The width of cast-ii-on gear faces for general pur- 
poses can be made to the following rule : 

Divide 8 hy the diametral pitch and add J" to the 
quotient; the sum will he xoidth of face for the pitch 
required. 

Example : What width of face for gear 4 P ? Divid- 
ing 8 by 4 and adding :J'' we obtain 2;^", for width of 
face. For change gears on lathes, where it is desira- 
ble not to have face very wide, the following rule can 
be used : 

Divide 4 hy the diametral pitch and add \" . 

By the latter rule a 4 P change gear would have but 
11" face. 
Speed of Gear The speed of gear cutters is subject to so many con- 
ditions that definite rules cannot be given. We append 
a table of average speeds. A coarse pitch cutter for 
pinion, 12 teeth, would usually be run slower than a 
cutter for a large gear of same pitch. 



PROVIDENCE, R. I. 



61 



TABLE OF AVERAGE SPEEDS FOR GEAR-CUTTERS. 



^ 




bO 


fcCC 


u 




c 


. = o 


5^ 

Is 


o 
« a; 


as 2 


M"1 




15 


s 




2 


5 iu. 


24 


18 


2* 


4i " 


30 


24 


3 


3||" 


36 


28 


4 


3f " 


42 


32 


5 


3tV " 


50 


40 


6 


2S" 


75 


55 


7 




85 


65 


8 


2^ " 


95 


75 


10 


^ " 


125 


90 


12 


2 " 


135 


100 


20 


H " 


145 


115 


32 


If '' 


160 


135 






025 in. 
,028 " 

031 " 
034 " 
037 " 

030 " 

032 " 
034 " 

026 " 
,027 " 

029 " 

031 '^ 



Feed to One 
Turn of Cutter 

in Wrought 
Iron and Steel. 


.011 


in. 


.013 




.015 




.017 




.019 


" 


.016 




.018 




.020 




.014 




.017 




.021 




.025 





t-. a a 
o.S Eg 



60 in. 
84 " 



1.12 
1.43 
1.85 
2.25 
2.72 
3.23 
3.25 
3.64 
4.20 
4.96 



o . 



^ 



.20 in 

.31 " 

.42 " 

.54 " 

.76 " 

.88 " 

1.17 " 

1.50 " 

1.26 " 

1.70 " 

2.41 " 

3.37 " 



In brass the speed of gear- cutters can be twice as -^^J^^^ ^'^ ^ ^ 
fast as in cast iron. Clock-makers and those making a 
specialty of brass gears exceed this rate even. A 12P 
cutter has been run 1,200 (twelve hundred) turns a 
minute in bronze. A 32 P cutter has been run 7,000 
(seven thousand) turns a minute in soft brass. 

In cutting 5 P cast-u-on gears, 75 teeth, a No. 1, 6 Pj^J^^J^^^p^^ 
cutter was run 136 (one hundred and thirty-six) turns 
a minute, roughing the spaces out the full 5 P depth ; 
the teeth were then finished with a 5 P cutter, running 
208 (two hundred and eight) turns a minute, feeding 
by hand. The cutter stood well, but, of course, the 
cast iron was quite soft. A 4 P cutter has finished 
teeth at one cut, in cast-iron gears, 86 teeth, running 48 
(forty-eight) tui'ns a minute and feeding y^^" at one 
turn, or 3 in. in a minute. 

Hence, while it is generally safe to run cutters as in 
the table, yet when many gears are to be cut it is well to 
see if cutters will stand a higher speed and more feed. 

In gears coarser than 4 P it is more economical to 
first cut the full depth wdth a stocking cutter and then 
finish with a gear cutter. This stocking cutter is made 



62 BROWN & SHARPE MFG. CO. 

on the principle of a circular splitting saw for wood. 
The teeth, however, are not set ; but side relief is ob- 
tained by making sides of cutter blank hollowing. The 
shape of stocking cutter can be same as bottom of 
spaces in a 12-tooth gear, and the thickness of cutter 
can be J of the circular pitch, see page 39. 
Keep Cutters The matter of keeping cutters sharp is so important 
that it has sometimes been found best to have the work- 
man grind them at stated times, and not wait until he 
can see that the cutters are dull. Thus, have him 
grind every two hours or after cutting a stated number 
of gears. Cutters of the style that can be ground 
upon their tooth faces without changing form are rap- 
idly destroyed if allowed to run after they are dull. 
Cutters are oftener wasted by trying to cut with them 
when they are dull than by too much grinding. Grind 
the faces radial with a free cutting wheel. Do not let 
the wheel become glazed, as this will draw the temper 
of the cutter. 

In Chapter YI. was given a series of cutters for cut- 
ting gears having 12 teeth and more. Thus, it was 
there implied that any gear of same pitch, having 135 
teeth, 136 teeth, and so on up to the largest gears, and, 
also, a rack, could be cut with one cutter. If this cut- 
ter is 4 P, we would cut with it all 4 P gears, having 
135 teeth or more, and we would also cut with it a 4 P 
rack. Now, instead of always referring to a cutter by 
the number of teeth in gears it is designed to cut, it 
has been found convenient to designate it by a letter 
or by a number. Thus, we call a cutter of 4 P, made 
to cut gears 135 teeth to a rack, inclusive, No. 1, 4 P. 

"We have adopted numbers for designating involute 
Involute Gear gear-cutters a-s in the following table : 

No. 1 will cut wheels from 135 teeth to a rack inclusive. 
a 2 << 



55 




134 teeth 


35 




54 " 


26 




34 " 


21 




25 " 


17 




20 '' 


14 




16 " 


12 




13 " 



PRO\^DENCE, E. I. 63 

By this plan it takes eight cutters to cut all gears 
having twelve teeth and over, of any one pitch. 

Thus it takes eight cutters to cut all involute 4 P 
gears having twelve teeth and more. It takes eight 
other cutters to cut all involute gears of 5 P, having 
12 teeth and more. A No. 8, 5 P cutter cuts only 5 P 
gears having 12 and 13 teeth. A No. 6, 10 P cutter 
cuts only 10 P geai's having 17, 18, 19 and 20 teeth. 
On each cutter is stamped the number of teeth at the 
limits of its range, as well as the number of the cutter. 
The number of the cutter relates only to the number 
of teeth in gears that the cutter is made for. 

In ordering cutters for involute spur-gears two things 
must be given : 

1. Either the number of teeth to he cut in the aear How to order 

. , ^ y Involute Cut- 

or the number of the cutter^ as given m the foregoing ters. 
table. 

2. Either the pitch of the gear or the diameter and 
number of teeth to be cut in the gear. 

If 25 teeth are to be cut in a 6 P involute ^ear, the 
cutter will be No. 5, 6 P, which cuts all 6 P gears from 
21 to 25 teeth inclusive. If it is desked to cut gears 
from 15 to 25 teeth, three cutters will be needed, No. 
5, No. 6 and No. 7 of the pitch required. If the pitch 
is 8 and gears 15 to 25 teeth are to be cut, the cutters 
should be No. 5, 8 P, No. 6, 8 P, and No. 7, 8 P. 

For each pitch of epicycloidal, or double-curve g-ears, Epicycioidai 

o^ LL T T .,-. , 'or Double- 

z^ cutters are made, in coarse-pitch gears, the varia- curve cutters. 
tion in the shape of spaces between gears of consecu- 
tive-numbered teeth is greater than in fine-pitch gears. 
A set of cutters for each pitch, to consist of so large a 
number as 24, has been established because double curve 
teeth have generally been preferred in coarse-pitch gears, 
though the tendency of late years is toward the involute 
form. 

Our double curve cutters have a guide shoulder on each 
side for the depth to cut. When this shoulder just reaches 
the periphery of the blank the depth is right. The marks 
which these shoulders make on the blank, should be as nar- 
row as can be seen, when the blanks are sized right. 



«4 



BROWN & SHAKPE MFG. CO. 



a Ji or 
Double - curve 
Gear Cutters. 



u 


B 


ii 


C 


a 


D 


« 


E 


(> 


F 


it 


G 


a 


H 


a 


I 


iC 


J 


a 


K 


u 


L 



N 


. ii 


30 " 33 " 





a 


34 " 37 " 


P 


a 


38 " 42 '• 


Q 


u 


43 " 49 " 


R 


(( 


50 "59 " 


S 


a 


60 " 74 " 


T 


u 


75 " 99 " 


II 


u 


100 " 149 « 


V 


a 


150 " 249 '' 


W 


ii 


250 " Rack. 


X 


a 


Rack. 



Double-curve gear-cutters are designated by letters 
instead of by numbers ; this is to avoid confusion in 
ordering. 

Following is the list of epicycloidal or double-curve 
gear-cutters :— 
cy^c1oid°ii^^Jr Cutter A cuts 12 teeth. Cutter M cuts 27 to 29 teeth. 

13 

14 

15 

16 

17 

18 

19 

20 

21 to 22 

23 to 24 

24 to 26 

A cutter that cuts more than one gear is made of 
proper form for the smallest gear in its range. Thus, 
cutter J for 21 to 22 teeth is correct for 21 teeth; 
cutter S for 60 to 74 teeth is correct for 60 teeth, 
and so on. 
Epic^cioidai ^^ Ordering epicycloidal gear-cutters designate the 
Cutters. letter of the cutter as in the foregoing table, also 

either give the pitch or give data that will enable us 
to determine the pitch, the same as directed for invo- 
lute cutters. 

More care is required in making and adjusting epi- 
cycloidal gears than in making involute gears. 
B?v^e*f ^Gear ^^ Ordering bevel-gear cutters three things must be 
given : 

1. The number of teeth in each gear. 

2. JEither the pitch of gears or the largest pitch 
diameter of each gear; see Fig. 16. 

3. The length of tooth face. 
If the shafts are not to run at right angles, it 

should be so stated, and the angle given. Involute 
cutters only are used for cutting bevel gears. No at- 
tempt should be made to cut epicyclodial tooth bevel gears 
with rotary disk cutters. 



Cutters. 



PROVIDENCE, E. I. 65 

In orderinfif -worm-wheel cutters, three things must „how to order 

° ' ° Worm -gear 

be given : Cutters. 

1. Nuniber of teeth in the toheel. 

2. Pitch of the icorni; see Chapter JlI. 

3. Whole diameter of worm. 

In any order connected with gears or gear-cutters, 
when the word *' Diameter " occurs, we usually under- 
stand that the pitch diameter is meant. When the 
whole diameter of a gear is meant it should be plainly 
written. Care in giving an order often saves the delay 
of asking fui'ther instructions. An order for one gear- 
cutter to cut from 25 to 30 teeth cannot be filled, be- 
cause it takes two cutters of involute form to cut from 
25 to 30 teeth, and three cutters of epicycloidal form 
to cut from 25 to 30 teeth. 

Sheet zinc is convenient to sketch gears upon, and 
also for making templets. Before making sketch, it is 
well to give the zinc a dark coating with the following 
mixtui'e : Dissolve 1 ounce of sulphate of copper (blue 
vitriol) in about 4 ounces of water, and add about one- 
half teaspoonful of nitric acid. Apply a thin coating 
with a piece of waste. 

This mixtiu'e will give a thin coating of copper to 
iron or steel, but the work should then be rubbed dry. 
Care should be taken not to leave the mixture where it 
is not wanted, as it rusts iron and steel. 

We have sometimes been asked why gears are noisy. In 
our own experience we have had less trouble with involute 
gears than we have had with epicyclodial gears, hut we have 
no experience in our own works with gears coarser than 4 P. 
Not many questions can be asked us to which we can give a 
less definite answer than to the question why gears are noisy ; 

We can indicate only some of the causes which may make 
gears noisy, such as: — depth of cutting not right — in this 
particular gears are oftener cut too deep than not deep 
enough ; cutting not central — this may make geers noisy in 
one direction when they are quiet while running in the other 
direction ; centre distance not right — if too deep the outer 
corners of the teeth in one gear may strike the fillets of the 
teeth in the other gear ; shafts not parallel ; frame of the 



66 BROWN & SHARPE MFG. CO. 

inacliine of sucli a form as to give off sound vibrations. Even 
-when we examine a pair of gears we cannot always tell what 
is the matter. 

Note. — For any pitch not in the following tables to find 
corresponding part : — multiply the tabular value for one inch 
by. the circular pitch required, and the product will be the 
value for the pitch given. Example : What is the value of s 
for 4 inch circular pitch? .3183 = s for r F and .3183 
X 4 = 1.2732 = 8 for 4" F. 

Note. — For an explanation of the expression -p", see 
page 17. 

The expression "Addendum and 1-P'" (addendum and a 
diameter pitch) means the distance of a tooth outside of pitch 
line and also the distance occupied for every tooth upon the 
diameter of pitch circle. 



PROVIDENCE, R. I. 



67 



Table of Chordal Thickness of Teeth for Gears and 
Cutters, on a Basis of 1 Diametral Pitch. 

EPICYCLOIDAIi. ' 





CHORDAL 


CORRECTED . 


CORRECTED S 


MAKK ON CUilii.K. 


THICKNESS. 


S-|-f FOR CUTT. 


FOR GEAR. 


A — 12T — IP 


1.5663 


1.1057 


1.0514 


B — 13T — IP 


1.5670 


1.1097 


1.0474 


C — 14T — IP 


1.5675 


1.1131 


1.0440 


r>__15T — IP 


1.5679 


1.1160 


1.0411 


E — 16T — IP 


1.5683 


1.1186 


1.0385 


F_17T — IP 


1.5686 


1.1209 


1.0362 


G — 18T — IP 


1.5688 


1.1229 


1.0342 


H_19T — IP 


1.5690 


1.1247 


1.0324 


1_20T — IP 


1.5692 


1.1263 


1.0308 


J_21T — IP 


1.5694 


1.1277 


1.0294 


K — 23T — IP 


1.5696 


1.1303 


1.0268 


L _ 25T — IP 


1.5698 


1.1324 


1.0247 


M — 27T — IP 


1.5699 


1.1343 


1.0228 


N — SOT — IP 


1.5701 


1.1363 


1.0208 


— 34T — IP 


1.5703 


1.1390 


1.0181 


P_38T — IP 


1.5703 


1.1409 


1.0162 


Q_43T — IP 


1.5705 


1.1428 


1.0143 


R_50T — IP 


1.5705 


1.1448 


1.0123 



SPECIAL, 



No. TEETH. 



IIT — IP 

lOT — IP 

9T — IP 



CHORDAL 
THICKNESS. 



1.5654 
1.5643 
1.5628 



.0559 
.0616 
.0684 



CORRECTED 
S-ff FOR CUTT. 



1.1012 
1.0955 

1.0887 



CORRECTED S 
FOR GEAR. 



1.0559 

1.0616 
1.0684 



INVOLUTE. 



No. CUTTER. 


CHORDAL 


CORRECTED 


CORRECTED S 


THICKNESS. 


S-f-f FOR CUTT. 


FOR GEAR. 


1_135T — IP 


1.5707 


1.1566 


1.0005 


2— 55T — IP 


1.5706 


1.1459 


1.0112 


3— 35T — IP 


1.5702 


1.1395 


1.0176 


4— 26T — IP 


1.5698 


1.1334 


1.0237 


5_ 21T — IP 


1.5694 


1.1277 


1.0294 


6_ 17T — IP 


1.5686 


1.1209 


1.0362 


7— 14T — IP 


1.5675 


1.1131 


1.0440 


8— 12T -IP 


1.5663 


1.1057 


1.0514 


IIT — IP 


1.5654 


1.1011 


1.0559 


lOT — IP 


1.5643 


1.0955 


1.0616 


9T — IP 


1.5628 


1.0887 


1.0684 


8T — IP 


1.5607 


1.0802 


1.0769 



For definition of chord see page 80. 



68 



BROWN & SUARPE MFG. CO. 



GEAE WHEELS. 



TABLE OF TOOTH PARTS CIRCULAR PITCH IN FIRST COLUMN. 



2 


Threads or 

Teeth per inch 

Linear. 


'3 

1.1 

p ■ 


Thickness of 

Tooth on 
Pitcli Line. 


a 
< 




kj 


la 


Width of 

Thread-Tool 

at End. 


o 


i^ 


p 


t 


s 


D^' 


s+f 


D"+/ 
1.3732 


P'x.31 


P'x.335 


i 


1.5708 


1.0000 


.0366 


1.2732 


.7366 


.6200 


.6700 


1* 


tV 


1.6755 


.9375 


.5968 


L.1937 


.6908 


1.2874 


.5813 


.6281 


If 


i 


1.7952 


.8750 


.5570 


1.1141 


.6445 


1.2016 


.5425 


.5863 


If 


_8_ 
1 3 


1.9333 


.8125 


.5173 


1.0345 


.5985 


1.1158 


.5038 


.5444 


u 


1 


2.0944 


.7500 


.4775 


.9549 


.5525 


1.0299 


.4650 


.5025 


iiV 


M 


2.1855 


.7187 


.4576 


.9151 


.5294 


.9870 


.4456 


.4816 


If 


A 


2.2848 


.6875 


.4377 


.8754 


.5064 


.9441 


.4262 


.4606 


lA 


if- 


2.3936 


.6562 


.4178 


.8356 


.4834 


.9012 


.4069 


.4397 


li 


i 


2.5133 


.6250 


.3979 


.7958 


.4604 


.8583 


.3875 


.4188 


h\ 


H 


2.6456 


.5937 


.3789 


.7560 


.4374 


.8156 


.3681 


.3978 


H 


f 


2.7925 


.5625 


.3581 


.7162 


.4143 


.7724 


.3488 


3769 


ItV 


H 


2.9568 


.5312 


.3382 


.6764 


.3913 


.7295 


.3294 


.3559 


1 


1 


3.1416 


.5000 


.3183 


.6366 


.3683 


,6866 


.3100 


.3350 


il 


ItV 


3.3510 


.4687 


.2984 


.5968 


.3453 


.6437 


.2906 


.3141 


i 


H 


3.5904 


.4375 


.2785 


.5570 


.3223 


.6007 


.2713 


.2931 


il 


ifV 


3.8666 


.4062 


.2586 


.5173 


.2993 


.5579 


.2519 


.2722 


i 


H 


4.1888 


.3750 


.2387 


.4775 


.2762 


.5150 


.2325 


.2513 


^J 


ifV 


4.5696 


.3437 


.2189 


.4377 


.2532 


.4720 


.2131 


.2303 


1 


li 


4.7124 


.3333 


.2122 


.4244 


.2455 


.4577 


.2066 


.2233 



PROVIDENCE, R. 



69 



TABLE OF TOOTH VKRT^.— Continued. 



CIRCULAR PITCH IN FIRST COLUMN. 



II 


Threads or 

Teeth per inch 

Linear. 




Thickness of 

Tooth on 
Pitch Line. 


< 


t 

p 


Depth of Space 

below 

Pitch Line. 


k 


Width of 

Thread-Tool 

at End. 


2-2 


P' 


1" 


P 


t 


s 


D" 


si-f 


D"+/. 


P'x.31 


P'x.335 


i 


If 


5.0265 


.3125 


.1989 


.3979 


.2301 


.4291 


.1938 


.2094 


tV 


1-2- 


5.5851 


.2812 


.1790 


.3581 


.2071 


.3862 


.1744 


.1884 


i 


2 


6.2832 


.2500 


.1592 


.3183 


.1842 


.3433 


.1550 


.1675 


tV 


2f 


7.1808 


.2187 


.1393 


.2785 


.1611 


.3003 


.1356 


.1466 


1 


2i 


7.8540 


.2000 


.1273 


.2546 


.1473 


.2746 


.1240 


.1340 


1 


2S 


8.3776 


.1875 


.1194 


.2387 


.1381 


.2575 


.1163 


.1256 


4 


3 


9.4248 


.1666 


.1061 


.2122 


.1228 


.2289 


.1033 


.1117 


tV 


3i 


10.0531 


.1562 


.0995 


.1989 


.1151 


.2146 


.0969 


.1047 


f 


3} 


10.9956 


.1429 


.0909 


.1819 


.1052 


.1962 


.0886 


.0957 


i 


4 


12.5664 


.1250 


.0796 


.1591 


.0921 


.1716 


.0775 


.0838 


f 


4i 


14.1372 


.1111 


.0707 


.1415 


.0818 


.1526 


.0689 


.0744 


\ 


5 


15.7080 


.1000 


.0637 


.1273 


.0737 


.1373 


.0620 


.0670 


h 


5J 


16.7552 


.0937 


.0597 


.1194 


.0690 


.1287 


.0581 


.0628 


\ 


6 


18.8496 


.0833 


.0531 


.1061 


.0614 


.1144 


.0517 


.0558 


+ 


7 


21.9911 


.0714 


.0455 


.0910 


.0526 


.0981 


.0443 


.0479 


4 


8 


25.1327 


.0625 


.0398 


.0796 


.0460 


.0858 


.0388 


.0419 


^ 


9 


28.2743 


.0555 


.0354 


.0707 


.0409 


.0763 


.0344 


.0372 


tV 


10 


31.4159 


.0500 


.0318 


.0637 


.0368 


.0687 


.0310 


.0335 


tV 


16 


50.2655 


.0312 


.0199'. 0398 


.0230 


.0429 


.0194 


.0209 



70 



BEOWN & SHAKPE MFG. CO. 



GEAE WHEELS. 

TABLE OF TOOTH PAKTS DIAMETRAL PITCH IN FIRST COLUMN. 



2 . 


5^ 


Thickness 
of Tooth on 
Pitch Line. 




k 

boo 


Depth of Space 

below 

Pitch Line. 


Id 

1' 


p 


P' 


t 


S 


D" 


^+/. 


D"+/. 


i 


6.2832 


8.1416 


2.0000 


4.0000 


2.3142 


4.3142 


i 


4.1888 


2.0944 


1.3333 


2.6666 


1.5428 


2.8761 


1 


3.1416 


1.5708 


1.0000 


2.0000 


1.1571 


2.1571 


li 


2.5133 


1.2566 


.8000 


1.6000 


.9257 


1.7257 


H 


2.0944 


1.0472 


.6666 


1.3333 


.7714 


1.4381 


If 


1.7952 


.8976 


.5714 


1.1429 


.6612 


1.2326 


2 


1.5708 


.7854 


.5000 


1.0000 


.5785 


1.0785 


2i 


1.3963 


.6981 


.4444 


.8888 


.5143 


.9587 


2i 


1.2566 


.6283 


.4000 


.8000 


.4628 


.8628 


2f 


1.1424 


.5712 


.3636 


.7273 


.4208 


.7844 


3 


1.0472 


.5236 


.3333 


.6666 


.3857 


.7190 


3i 


.8976 


.4488 


.2857 


.5714 


.3306 


.6163 


4 


.7854 


.3927 


.2500 


.5000 


.2893 


.5393 


5 


.6283 


.3142 


.2000 


.4000 


.2314 


.4314 


6 


.5236 


.2618 


.1666 


.3333 


.1928 


.3595 


7 


.4488 


.2244 


.1429 


.2857 


.1653 


.3081 


8 


.3927 


.1963 


.1250 


.2500 


.1446 


.2696 


9 


.3491 


.1745 


.1111 


.2222 


.1286 


.2397 


10 


.3142 


.1571 


.1000 


.2000 


.1157 


.2157 


11 


.2856 


.1428 


.0909 


.1818 


.1052 


.1961 


12 


.2618 


.1309 


.0833 


.1666 


.0964 


.1798 


13 


.2417 


.1208 


.0769 


.1538 


.0890 


.1659 


14 


.2244 


.1122 


.0714 


.1429 


.0826 


.1541 



PROVIDENCE, R. I. 



71 



TABLE OF TOOTH TAUTS— Continued, 



DIAMETRAL PITCH IN FIRST COLUMN. 



2 . 
II 




Thickness 
of Tooth on 
Pitch Line. 




6 
ft 

fcJDo 

r 


Depth of Space 

below 

Pitch Line. 


6 


P. 


P'. 


t. 


s. 


D". 


s+f. 


D"4-/. 


15 


.2094 


.1047 


.0666 


.1333 


.0771 


.1438 


16 


.1963 


.0982 


.0625 


.1250 


.0723 


.1348 


17 


.1848 


.0924 


.0588 


.1176 


.0681 


.1269 


18 


.1745 


.0873 


.0555 


.1111 


.0643 


.1198 


19 


.1653 


.0827 


.0526 


.1053 


.0609 


.1135 


20 


.1571 


.0785 


.0500 


.1000 


.0579 


.1079 


22 


.1428 


.0714 


.0455 


.0909 


.0526 


.0980 


24 


.1309 


.0654 


.0417 


.0833 


.0482 


.0898 


26 


.1208 


.0604 


.0385 


.0769 


.0445 


.0829 


28 


.1122 


.0561 


.0357 


.0714 


.0413 


.0770 


30 


.1047 


.0524 


.0333 


.0666 


.0386 


.0719 


32 


.0982 


.0491 


.0312 


.0625 


.0362 


.0674 


34 


.0924 


.0462 


.0294 


.0588 


.0340 


.0634 


36 


.0873 


.0436 


.0278 


.0555 


.0321 


.0599 


38 


.0827 


.0413 


.0263 


.0526 


.0304 


.0568 


40 


.0785 


.0393 


.0250 


.0500 


.0289 


.0539 


42 


.0748 


.0374 


.0238 


.0476 


.0275 


.0514 


44 


.0714 


.0357 


.0227 


.0455 


.0263 


.0490 


46 


.0683 


.0341 


.0217 


.0435 


.0252 


.0469 


48 


.0654 


.0327 


.0208 


.0417 


.0241 


.0449 


50 


.0628 


.0314 


.0200 


.0400 


.0231 


.0431 


56 


.0561 


.0280 


.0178 


.0357 


,0207 


.0385 


60 


.0524 


.0262 


.0166 


.0333 


.0193 


.0360 



PART II. 



CHAPTER I. 
TANGENT OF ARC AND ANGLE. 



In Part II. we shall show how to calculate some ^l^gSed.'^ ^* 
of the functions of a right-angle triangle from a table 
of circular functions, the application of these calcula- 
tions in some chapters of Part I. and in sizing blanks 
and cutting teeth of spkal gears, the selection of 
cutters for spkal gears, the application of continued 
fractions to some problems in gear wheels and cutting 
odd screw-thi'eads, etc., etc. 

A. Function is a quantity that depends upon another 
quantity for its value. Thus the amount a workman 
earns is a function of the time he has worked and of fl^d?'^*^^^ ^®' 
his wages per hour.* 




In any right- angle triangle^ O A B, we shall, for Right -angle 
convenience, call the two lines that form the right 
angle O A B the sides^ instead of base and perpen- 
dicular. Thus O A B, being the right angle we call 
the line O A a side, and the line A B a side also. 

When we speak of the angle A O B, we call the line 
O A the side adjacent. When we are speaking of the ^^^^ adjacent. 
angle A B O we call the line A B the side adjacent. 
The line opposite the right angle is the hypothenuse. Hypothenuse. 



74 

Tangent. 



BBOWN & SHARPS MFG. CO. 

The Tangent of an arc is the line that touches it at 
one extremity and is terminated by a line drawn from 
the center through the other extremity. The tangent 
is always outside the arc and is also perpendicular to 
the radius which meets it at the point of tangency. 




]Fig. 30 

Thus, in Fig. 30, the line A B is the tangent of the arc 
A C. The point of tangency is at A. 

An angle at the center of a circle is measured by the 
arc intercepted by the sides of the angle. Hence the 
tangent A B of the arc A C is also the tangent of the 
angle A O B. 

In the tables of circular functions the radius of the 
arc is unity, or, in common practice, we take it as one 
inch. The radius O A being 1", if we know the length 
of the line or tangent A B we can, by looking in a 
table of tangents, find the number of degrees in the 
angle A O B. 
To find the Thus, if A B is 2.25" long, we find the angle A O B 

Degrees in an ^ °' ^ 

Angle. is 66 very nearly. That is, having found that 2.2460 

is the nearest number to 2.25 in the table of tangents 
at the end of this volume, we find the corresponding 
degrees of the angle in the column at the left hand of 
the table and the minutes to be added at the top of 
the column containing the 2.2460. 

The table gives angles for every 10', which is suf- 
ficient for most purposes. 



PROVIDENCE, R. I. 75 

Now, if we have a right-angle triangle with an angle 
the same as O A B, but with O A two inches long, the 
Hne A B will also be twice as long as the tangent of 
angle A O B, as found in a table of tangents. 

Let us take a triangle with the side O A = 5" long, ^^f ^^^i^j^ t*^ 
and the side A B = 8" long ; what is the number of |ree^« ^^ ^^ 
degrees in the angle A B ? 

Dividing 8" by 5 we find what would be the length 
of A B if O A was only 1" long. The quotient then 
would be the length of tangent when the radius is 1" 
long, as in the table of tangents. 8 divided by 5 is 
1.6. The nearest tangent in the table is 1.6003 and 
the corresponding angle is 58°, which would be the 
angle A O B when A B is 8" and the radius O A is 5" 
very nearly. The difference in the angles for tangents 
1.6003 and 1.6 could hardly be seen in practice. The 
side opposite the requked acute angle corresponds to 
the tangent and the side adjacent corresponds to the 
radius. Hence the rule : 

To find the tangent of either acute angle in a right- r^^^^^^ *^® 
angle triangle : Divide the side opposite the angle by 
the side adjacent the angle and the quotient loill he 
the tangent of the angle. This rule should ba com- 
mitted to memory. Having found the tangent of the 
angle, the angle can be taken from the table of tan- 
gents. 

The complement of an angle is the remainder after Complement 
subtracting the angle from 90°. Thus 40° is the com- 
plement of 50°. 

2'he Cotangent of an angle is the tangent of the cotangent. 
complement of the angle. Thus, in Fig. 30, the line 
A B is the cotangent of A O E. In right-angle tri- 
angles either acute angle is the complement of the 
other acute angle. Hence, if we know one acute angle, 
by subtracting this angle from 90° w^e get the other 
acute angle. As the arc approaches 90° the tangent 
becomes longer, and at 90° it is infinitely long. 

The sign of infinity is oo. Tangent 90° =: oo. 



76 BROWN & SHARPE MFG. CO. 

Angie^^bT\he ^J ^ ^^^^^ ^f tangents, angles can be laid out upon 
'^nTle^Fi ^32 ' ^^^®^ zinc, etc. This is often an advantage, as it is not 
convenient to lay protractor flat down so as to mark 
angles up to a sharp point. If we could lay off the 
length of a line exactly we could take tangents direct 
from table and obtain angle at once. It, however, is 
generally better to multiply the tangent by 5 or 10 
and make an enlarged triangle. If, then, there is a 
slight error in laying off length of lines it will not 
make so much difference with the angle. 

Let it be required to lay off an angle of 14° 30'. By 
the table we find the tangent to be .25861. Multiply- 
ing .25861 by 5 we obtain, in the enlarged triangle, 
1.29305" as the length of side opposite the angle 14° 
30'. As we have made the side opposite five times as 
large, we must make the side adjacent five times as 
large, in order to keep angle the same. Hence, Fig. 
31, draw the line A B 5" long ; perpendicular to this 
line at A draw the line A O 1.293" long ; now draw the 
line O B, and the angle ABO will be 14° 30'. 

If special accuracy is required, the tangent can be 
multiplied by 10; the line A O will then be 2.586" long 
and the line A B 10" long. Kemembering that the 
acute angles of a right-angle triangle are the comple- 
ments of each other, we subtract 14° 30' from 90' and 
obtain 75° 30' as the angle of A O B. 

The reader will remember these angles as occurring 
in Part I., Chapter IV., and obtained in a different 
way. A semicircle upon the line O B touching the 
extremities O and B will just touch the right angle at 
A, and the line O B is four times as long as O A. 

Let it be required to turn a piece 4" long, 1" diam- 
eter at small end, with a taper of 10° one side with the 
other ; what will be the diameter of the piece at the 
large end ? 

A section. Fig. 32, through the axis of this piece is 
j)-^^ et^^r ^of *a ^^® Same as if we added two right-angle triangles, O 
Ta pe r i n g A B and O' A' B', to a straiefht piece A' A B B', 1" 

piece. Fig. 33. o jr 

wide and 4" long, the acute angles B and B' being 5°, 
thus making the sides O B and O' B' 10° with each 
other. 



PROVIDENCE, E. I. 



%^ 




-1-.293-+- 

Eig. iil. 




I^ig. 32 



78 BROWN & SHARPE MFG. CO. 

The tangent of 5° is .08748, which, multiplied by 
4", gives .34992" as the length of each line, A O and 
A' O', to be added to 1" at the large end. Taking 
twice .34992'' and adding to 1" we obtain 1.69984" as 
the diameter of large end. 

This chapter must be thoroughly studied before taking up 
the next chapters. If once the memory becomes confused 
as to the tangent and sine of an angle, it will take much 
longer to get righted than it will to first carefully learn to 
recognize the tangent of an angle at once. 

If one knows what the tangent is, he can better tell 
the functions that are not tangents. 



PROAIDENCE, R. I. 



T9 



CHAPTER II. 

SIKE— COSINE AND SECAHT : SOME OF THEIR APPLICATIONS IN 
MACHINE CONSTRUCTION. 



The Sine of an arc is the line drawn from one 
extremity of the arc to the diameter passing through 
the other extremity, the hne being perpendicular to 
the diameter. 

Another definition is : The sine of an arc is the dis- 
tance of one extremity of the arc from the diameter, 
through the other extremity. 

The sine of an angle is the sine of the arc that ^^^^^^ jj^ ^^^ 
measures the angle. 

In Fig. 33 , A C is the sine of the arc B C, and of 
the angle B O C. It will be seen that the sine is 
always inside of the arc, and can never be longer than 
the radius. As the arc ap- 
proaches 90°, the sine comes 
neai'er to the radius, and at 90° 
the sine is equal to 1, or is the 
radius itself. From the defini- 
tion of a sine, the side A C, 
opposite the angle A O C, in 
any right-angle triangle, is the 
sine of the angle A O C, when 
O C is the radius of the arc. 
Hence the rule : In any right-angle triangle, the side 
opposite either acute angle, divided hy the hypothe- 
nuse, is equal to the sine of the angle. 

The quotient thus obtained is the length of side 
opposite the angle when the hypothenuse or radius is 
unity. The rule should be carefully committed to 
memory. 



E 


5 


C 


\ 


/ 


A 





E 1 



Fig. 33- 



To find the 
Sine. 



80 



BEOWN & SHARPE MFG. CO. 



^hord of an ^ Chord is a straight line joining the extremities of 
an arc, and is twice as long as the sine of half the 
angle measured by the arc. Thus, in Fig. 34, the 
chord F C is twice as long as the sine A C. 




find 



Kig. 34- 

Let there be four holes equidistant about a circle 
3" in diameter — Fig. 34 ; what is the shortest distance 
between two holes ? This shortest distance is the 
id'lhTchord? chord A B, which is twice the sine of the angle COB. 
The angle A O B is one -quarter of the circle, and 
C O B is one-eighth of the circle. 360°, divided by 
8=45°, the angle COB. The sine of 45° is .70710, 
which multiplied by the radius 1.5", gives length C B in the 
circle, 3'' in diameter, as 1.06065". Twice this length is 
the required distance A B=2.1213". 

When a cylindrical piece is to be cut into any num- 
ber of sides, the foregoing operation can be applied to 
obtain the width of one side. A plane figure bounded 
by straight lines is called a polygon. 



Polygon. 



PKOVIDENCE, R. I. 



81 



When the outside diameter and the number of sides of 
a regular polygon are given, to find the length of 
one of the sides : Divide ^&^° by tioice the number of To find th© 

. . "^ ^ length of Side. 

Sides ; 'multiply the sine of the quotient by the outer 

diameter , and the product loill be the length of one of 

the sides. 

Multiplying by the diameter is the same as multi- 
plying by the radius, and that product again by 2. 

The Cosine of an angle is the sine of the comple- Cosine, 
ment of the angle. 

In Fig. 33 , C O D is the complement of the angle 
A O C ; the line C E is the sine of COD, and hence 
is the cosine of B O C. The line O A is equal to C E. 
It is quite as well to remember the cosine as the part 
of the radius, from the center that is cut off by the 
sine. Thus the sine A C of the angle A O C cuts off 
the cosine O A. The line O A may be called the 
cosine because it is equal to the cosine C E. 

In any right-angle triangle, the side adjacent either 
acute angle corresponds to the cosine when the 
hypothenuse is the radius of the arc that measures 
the angle; hence: Divide the side adjacent the acute To And the 
angle by the hypothenuse^ and the quotient will be the 
cosine of the angle. 

"WTien a cylindrical piece is cut into a polygon of 

any number of sides, a table of cosines can be used to .i^®^f *^ ^^ 
"J ' ^ sides of Poly- 

get the diameter across the sides. go^- 




82 



BROWN & SHARPE MFG. CO. 



Let a cylinder, 2" diameter, Fig. 36, be cut six-sided ; 
wliat is the diameter across the sides ? 

The angle A O B, at the center, occupied by one of 
these sides, is one-sixth of the circle, =60°. The 
cosine of one-half this angle, 30°, is the line C O; 
twice this line is the diameter across the sides. The 
cosine of 30° is .86602, which, multiplied by 2, gives 
1.73204" as the diameter across the sides. 

Of course, if the radius is other than unity, the cosine 
should be multiplied by the radius, and the product 
again by 2, in order to get diameter across the sides ; 
or what is the same thing, multiply the cosine by the 
whole diameter or the diameter across the corners. 

The rule for obtaining the diameter across sides of 
sides of a Poly- regular polygon, when the diameter across corners is 
given, will then be: Multiply the cosine of 360°^ 
divided by twice the number of sides, by the diameter 
across corners, and the product will be the diameter 
across sides. 

Look at the right-hand column for degrees of the 
cosine, and at bottom of page for minutes to add to 
the degrees. 

The Secant of an arc is a straight line drawn from 
the center through one end of an arc, and terminated 
by a tangent drawn from the other end of the arc. 

Thus, in Fig. 36, the line O B is the secant of the 
angle COB. 

A C B 



Rule for Di- 
ameter across 



Secant. 




To find 
Secant. 



In any right-angle triangle, divide the hypothenuse 
by the side adjacent either acute angle, and the quO' 
tient will be the secant of that angle. 



PRO'SaDENCE, K. I. 83 

That is, if we divide the distance OB by O C, in 
the right-angle triangle COB, the quotient will be 
the secant of the angle COB. 

The secant cannot be less than the radius ; it in- 
creases as the angle increases, and at 90° the secant is 
infinity=x . 

A six-sided piece is to be H" across the sides ; how^ .''^^j^'^^^*^* 
large must a blank be turned before cutting the sides ? J^a Poi^'Su^* 
Dividing 360° by twice the number of sides, we have 
30°, which is the angle COB. The secant of 30° is 
1.1547. 

The radius of the six-sided piece is .75". 

Multiplying the secant 1.1547 by .75", we obtain the 
length of radius of the blank O B ; multiplying again 
by 2, we obtain the diameter 1.732" -f-. 

Hence, in a regular polygon, when the diameter 
across sides and the number of sides are given, to find 
diameter across corners : Multiply the secant of 360° 
divided by ticice the number' of sides, by the diameter 
across sides, and the product loill be the diameter 
across corners. 

It will be seen that the side taken as a divisor has 
been in each case the side corresponding to the radius 
of the arc that subtends the angle. 



84 BROWN & SHAEPE MFG. CO. 



CHAPTER III. 

APPLICATIOM OF CIRCULAR FUNCTIONS— WHOLE DIAMETER OF 
BEYEL GEAR BLANKS— ANGLES OF BEVEL GEAR BLANKS. 



To avoid confusion we will illustrate one gear only. 
The same rules apply to all sizes of bevel gears. Fig. 
31 is the outline of a pinion 4 P, 20 teeth, to mesh with 
a gear 28 teeth, shafts at right angles. For making 
sketch of bevel gears see Chapter IX., Part I. 

In Fig. 31, the line O m' m is continued to the line 
a h. The angle c' O i that the cone pitch-line makes 
with the center line may be called the center angle. 
Angle of The center angle c O i is equal to the angle of edge 
' ' c i c. c' i is the side opposite the center angle c' O 
i, and c' O is the side adjacent the center angle, c' 
i = 2.5"; & O = 3.5". Dividing 2.5" by 3.5" we 
obtain .71428" + as the tangent of e' O ^. In the table 
we find .71329 to be the nearest tangent, the corre- 
sponding angle being 35° 30'. 35 J°, then, is the center 
angle c O i and the angle of edge c i 7i, very nearly. 

When the axes of bevel gears are at right angles the 
angle of edge of one gear is the complement of angle 
of edge of the other gear. Subtracting, then, 35|^° 
from 90° we obtain 54 J° as the angle of edge of gear 
28 teeth, to mesh with gear 20 teeth, Fig. 37, from which we 
have the rule for obtaining centre angles when the axes of 
gears are at right angles. 

Divide the radius of the pinion by the radius of the gear 
and the quotient will be the tangent of centre angle of the 
pinion. 

Now subtract this centre angle from 90 deg. and we have 
the centre angle of the gear. 

The same result is obtained by dividing the number of 
teeth in the pinion by the number of teeth in the gear ; the 
quotient is the tangent of the centre angle. 



PROVIDENCE, B. I. 



85 




86 BROWN & SHARPE MFG. CO. 

Angle Of Face. To obtain angle of face O m' c', the distance c O 
becomes the side opposite and the distance m" c is 
the side adjacent. 

The distance c O is 3.5", the radius of the 28 tooth 
bevel gear. The distance c m" is by measurement 
2.82'^ 

Dividing 3.5 by 2.82 we obtain 1.2411 for tangent 
of angle of face O m" e. The nearest tangent in the 
table is 1.2422 and the corresponding angle is 51° 10'. 
To obtain cutting angle c O n" we divide the distance 
c' n' by c O. By measurement c' n" is 2.2". Divid- 
ing 2.2 by 3.5 we obtain .62857 for tangent of cutting 
angle. The nearest corresponding angle in the table 
is 32°10'. 

The largest pitch diameter, kj, of a bevel gear, as in 
Fig. 38, is known the same as the pitch diameter of 
any spur gear. Now, if we know the distance h o or 
its equal a q^ we can obtain the whole diameter of 
bevel gear blank by adding twice the distance h o to 
the largest pitch diameter. 
cremen^^Vig" Twice the distance h o, or what is the same thing, 
2^- the sum oi a q and 5 o is called the diameter incre- 

ment^ because it is the amount by which we increase 
the largest pitch diameter to obtain the whole or out- 
side diameter of bevel gear blanks. The distance h o 
can be calculated without measuring the diagram. 

The angle b o J is equal to the angle of edge. 

The angle of edge, it will be remembered, is the 
angle formed by outer edge of blank or ends of teeth 
with the end of hub or a plane perpendicular to the 
axis of gear. 

The distance ^ o is equal to the cosine of angle of 
edge, multiplied by the distance j o. The distance J o 
is the addendum, as in previous chapters ( — s). 

Hence the rule for obtaining the diameter increment 
of any bevel gear: Multiply the cosine of angle of 
edge by the xoorking depth of teeth (D"), and the 
product will be the diameter increment. 

By the method given in Chapter II. we find the 

angle of edge of gear (Fig. 38) is 56° 20'. The cosine 

of 56° 20° is .55436, which, multiplied by |", or the 

^Outside Diana- (Jepth of the 3 P gear, gives the diameter increment of 

the bevel gear 18 teeth, 3 P meshing with pinion of 12 



PKO-STEDENCE, K. I. 



87 




88 BROWN & SHARPE MFG. CO. 

teeth. I of .55436=.369" + (or .37", nearly). Adding 
the diameter increment, .37", to the largest pitch 
diameter of gear, 6", we have 6.37" as the outside 
diameter. 

In the same manner, the distance c J is half the 
diameter increment of the pinion. The angle c d h is 
equal to the center angle of pinion, and when axes are 
at right angles is the complement of center angle of 
gear. The center angle of pinion is 33° 40'. The 
cosine, multiplied by the working depth, gives .555" 
for diameter increment of pinion, and we have 4.555" 
for outside diameter of pinion. 

In turning bevel gear blanks, it is sufficiently accu- 
rate to make the diameter to the nearest hundredth of 
an inch. 
Angle lucre- The Small angle o O j' is called the angle increment. 
When shafts are at right angles the face angle of one 
gear is equal to the center angle of the other gear, 
minus the angle increment. 

Thus the angle of face of gear (Fig. 38) is less than 
the center angle D O ^, or its equal O j khj the angle 
o OJ. That is, subtracting o OJ from Oj k, the re- 
mainder will be the angle of face of gear. 

Subtracting the angle increment from the center 
angle of gear, the remainder will be the cutting 
angle. 

The angle increment can be obtained by dividing 
o j\ the side opposite, by O^', the side adjacent, thus 
finding the tangent as usual. 

The length of cone-pitch line from the common 
center, O to J, can be found, without measuring dia- 
gram, by multiplying the secant of angle O J k, or the 
center angle of pinion, by the radius of largest pitch 
diameter of gear. 

The secant of angle OJ k, 33° 40', is 1.2015, which, 
multiplied by 3", the radius of gear, gives 3.6045" as 
the length of line O J. 

Dividing oJ by OJ, we have for tangent .0924, and 
for angle increment 5° 20'. 

The angle increment can also be obtained by the 
following rule : 



PROVIDENCE, R. T. g^ 

Divide the sine of ^center angle by half the num^ 
her of teeth, and the quotient loill be the tangent of 
increment angle. 

Subtracting the angle increment from center angles 
of gear and pinion, we have respectively ; 
Cutting angle of gear, 51°. 
Cutting angle of pinion, 28° 20'. 

Eemembering that when the shafts are at right 
angles, the face angle of a gear is equal to the cutting 
angle of its mate (Chapter X. part 1), we have : 
Face angle of gear, 28° 20'. 
Face angle of pinion, 51°. 

It will be seen that both the whole diameter and the 
angles of bevel gears can be obtained without making 
a diagram. Mr. George B. Grant has made a table of 
different pairs of gears from 1 to 1 up to 10 to 1, con- 
taining diameter increments, angle increments and 
center angles, and has published it in the American 
Machinist of October 31, 1885. We have adopted the 
terms " diameter increment," " angle increment " and 
^' center angle " from him. He uses the term " back 
angW for what we have called angle of edge, only he 
measures the angle from the axis of the gear, instead ^^^^ ^^^ ^^ 
of from the side of the gear or from the end of hub, Angle by the 
as we have done ; that is, his "back angle" is the com- 
plement of our angle of edge. 

In laying out angles, the following method may be 
preferred, as it does away with the necessity of making 
a right angle : Draw a circle, ABO (Fig. 39), ten 




IfHg:. 39 



^^ BROWN & SHARPE MFG. CO. 

inches in diameter. Set the dividers to ten times the 
sine of the required angle, and point off this distance 
in the circumference as at A B. From any point O in 
the circumference, draw the lines O A and O B. The 
angle A O B is the angle required. Thus, let the re- 
quired angle be 12°. The sine of 12° is .20791, which, 
multiplied by 10, gives 2.0791", or ^jf^" nearly, for 
the distance A B. 

Any diameter of circle can be taken if we multiply 
the sine by the diameter, but 10" is very convenient, 
as all we have to do with the sine is to move the 
decimal point one place to the right. 

If either of the lines pass through the centre, then the 
two lines which do not pass through the centre will form a 
right angle. Thus, if B passes through the centre then 
the two lines A B and A will form a right ande at A. 



PROVIDENCE. R. I. 91 



CHAPTER IV. 
SPIRAL GEARS— CALCDLATIOHS FOR PITCH OF SPIRALS. 



When the teeth of a gear are cut, not in a straight Spiral Gear, 
path, like a spur gear, but in a hehcal or screw-like 
path, the gear is called, technically, a twisted or screw 
gear, but more generally among mechanics, a spiral 
gear. A distinction is sometimes made between a 
screw gear and a twisted gear. In twisted gears the 
pitch sui'faces roll upon each other, exactly like spur 
gears, the axes being parallel, the same as in Fig. 1, 
Part I. In screw gears there is an end movement, 
or slipping of the pitch surfaces upon each other, the 
axes not being parallel. In screw gearing the action 
is analogous to a screw and nut, one gear driving 
another by the end movement of its tooth path. This 
is readily seen in the case of a worm and worm-wheel, 
when the axes are at right angles, as the movement of 
wheel is then wholly due to the end movement of 
worm thread. But, as we make the axes of gears more 
nearly parallel, they may still be screw gears, but the 
distinction is not so readily seen. 

We can have two gears that are alike run together, 
with their axes at right angles, as at A B, Fig. 41. 

The same gear may be used in a train of screw gears 
or in a train of twisted gears. Thus, B, as it relates to 
A, may be called a screw gear; but in connection with 
C, the same gear, B, may be called a twisted gear. 
These distinctions are not usually made, and we call 
all helical or screw-like gears made on the Universal 
Milling Machine spiral gears. 

When two external spiral gears run together, with Direction of 
their axes parallel, the teeth of the gears must have ereuce to Axes, 
opposite hand spirals. ^^' 



92 



BROWN & SHARPE MFG. CO. 



Thus, in Fig. 41 the gear B has right hand spiral 
teeth, and the gear C has left hand spiral teeth. When 
the axes of two spiral gears are at right angles, both 
gears must have the same hand spiral teeth. A and 
B, Fig. 41, have right hand spiral teeth. If both gears 
A and B had left hand spiral teeth, the relative direc- 
tion in which they turn would be reversed. 

Spiral Pitch. ijij^g spiral pitch or pitch of spiral is the distance the 
spiral advances in one turn. Strictly, this is the lead 
of the spiral. A cylinder or gear cut with spiral 
grooves is merely a screw of coarse pitch or long lead ; 
that is, a spiral is a coarse pitch screw, and a screw is 
a fine pitch spiral. 

Since the introduction and extensive use of the 
Universal Milling Machine, it has become customary 
to call any screw cut in the milling machine a spiral. 
The spiral pitch is given as so many inches to one 
turn. Thus, a cylinder having a spiral groove that ad- 
vances six inches to one turn, is said to have a six inch 
spiral. 

In screws the pitch is often given as so many threads 
to one inch. Thus, a screw of ^' lead is said to be 
2 threads to the inch. The reciprocal expression is 
not much used with spirals. For example, it would 
not be convenient to speak of a spiral of 6'' lead, as -J- 
threads to one inch. 

The calculations for spirals are made from the func- 
tions of a right angle triangle. 
Example, Cut from paper a right angle triangle, one side of 

ture of a Helix the right angle 6" long, and the other side of the 
pi^^ • right angle 2". Make a cylinder 6" in circumference. 
It will be remembered (Part I., Chapter II.) that the 
circumference of a cylinder, multiplied by .3183, equals 
the diameter— 6" X. 3183=1.9098". Wrap the paper 
triangle around the cylinder, letting the 2" side be 
parallel to the axis, the 6" side perpendicular to the 
axis and reaching around the cylinder. The hypoth- 
eneuse now forms a helix or screw-like line, called 
a spiral. Fasten the paper triangle thus wrapped 
around. See Fig. 42. 



PKOVIDENCE, E. I. 



93 




Fig. 40.-RACKS AND GEARS. 




Fig. 41,-SPIRAL GEARING. 



94 



BKOWN & SHAEPE MFG. CO. 




JFig.. 43 



If we now turn this cylinder A B C D in the direc- 
tion of the arrow, the spiral will advance from O to E. 
This advance is the pitch of the spiral. 

The angle EOF, which the spiral makes with the 
axis E O, is the angle of the spiral. This angle is 
found as in Chapter I. The circumference of the 
cylinder corresponds to the side opposite the angle. 
The pitch of the spiral corresponds to the side adjacent 
the angle. Hence the rule for getting angle of spiral : 
Kuiesforcai- Divide the circumference of the cylinder or spiral 

culating the J ^ iJ , / 

parts of a Spi- by the number of inches of spiral to one turn, and the 
quotient will be the tangent of angle of spiral. 

When the angle of spiral and circumference are 
given, to find the pitch : 

Divide the circumference by the tangent of angle, 
and the quotient will be the pitch of the spiral. 

When the angle of spiral and the lead or pitch of 
spiral are given, to find the circumference : 

Multiply the tangent of angle hy the pitch, and the 
product will be the circumference. 

When applying calculations to spiral gears the angle is 
reckoned at the pitch circumference and not at the outer or 
addendum circle. 

It will be seen that when two spirals of different diame- 
ters have the same pitch the spiral of less diameter will have 
the smaller angle. Thus in Fig. 42 if the paper triangle had 
been 4'' long instead of ^" the diameter of the cylinder would 
have been 1.27^' and the angle of the spiral would have been 
only 32 J degrees. 



PEOTXDENCE, R. t. 



95 



CHAPTER V. 

EXAMPLES IH CALCOLATION OF PITCH OF SPIRAL— ANGLE OF 

SPIRAL— CIRCUMFERENCE OF SPIRAL GEARS— 

A FEW HINTS ON CUTTING. 



It will be seen that the rules for calculating circum- 
ference of spiral gears, angle and pitch of spiral are 
the same as in Chapter I, for tangent and angle of a right 
angle triangle. In Chapter IV the word " circumference" 
is substituted for " side opposite," and the words "pitch of 
spiral" are substituted for side " adjacent." 

When two spiral gears are in mesh the angle of i.ai?wUh*ref er' 
spii'al should be the same in one gear as in the other, ^^^^ ^^ Anglo 
in order to have the shafts parallel and the teeth work 
properly together. When two gears both have right 
hand spii'al teeth, or both have left hand spiral teeth, 
the angle of their shafts will be equal to the swm of 
the angles of their spirals. But when two gears have 
different hand spirals the angle of their shafts will be 
equal to the difference of their angles of spirals. 
Thus, in Fig. 41 the gears A and B both have right 
hand spirals. The angle of both spirals is 45°, their 
sum is 90°, or their axes are at right angles. But C 
has a left hand spiral of 45°. Hence, as the difference 
between angles of spirals of B and C is 0, their axes 
are parallel. 

When the two gears have the same number of teeth 
the pitch of the spiral will be alike in both gears. But 
when one gear has more teeth than the other the pitch 
of spiral in the larger gear should be longer in the 
same ratio. Thus, if one gear has 50 teeth and the pitch in SpU 
other gear has 25 teeth, the pitch of spiral in the 50 Diameters, 
tooth wheel should be twice as long as that of the 25 



S6 BROWN & SHAKPE MFG. CO. 

tooth wheel. Of course, the diameter of pitch circle 
should be twice as large in the 50 tooth as in the 25 
tooth wheel. 

In spirals where the angle is 45° the circumference 
is the same as the spiral pitch, because the tangent of 
4:5° is 1. 
ciSTrnfeJence Sometimes the circumference is varied to suit a 
tosuitaspirai. pitch that Can be cut on the machine and retain the 
angle requu'ed. This would apply to cutting rolls for 
making diamond-shaped impressions where the diam- 
eter of the roll is not a matter of importance. 

When two gears are to run together in a given 
velocity ratio, it is well to first select spirals that the 
machine will cut of the same ratio, and calculate the 
numbers of teeth and angle to correspond. This will 
often save considerable time in figuring. 

The calculations for spiral gears present no special 
difficulties, but sometimes a little ingenuity is required 
to make work conform to the machine and to such 
cutters as we may have in stock. It is a good plan to 
make a trial piece for each gear, and to cut a few teeth 
in each trial piece to test the setting of the machine. 
Dummies or Thcsc trial picccs are called " dummies." If the gears 
are likely to be duplicated, each dummy can be marked 
and kept for f ature setting of the machine. Stamp all 
the data on the dummies ; it is better to spend a little 
time in marking dummies than a good deal of time 
hunting up, or trying to remember^ old data. 

Let it be required to make two spiral gears to run 
with a ratio of 4 to 1, the distance between centers to 
be 3.125" (31"). 

By rule given in Chapter XII., Part I., we find the 
diameters of pitch circles will be 5" and IJ". Let us 
take a spiral of 48" pitch for the large gear, and a 
spiral of 12" pitch for the small gear. The circumfer- 
ence of the 5" pitch circle is 15.70796". Dividing 
the circumference by the pitch of the spiral, we have 
i5-T^o^T9 6 _32724^^ for tangent of angle of spiral. In 
the table the nearest angle to tangent, .32724'', is 18° 10'. 
As before stated, the angle of the teeth in the small 
gear will be the same as the angle of teeth or spiral in 



PROVIDENCE, R. I. 97 

the lar^e sfear. Nott, this rule efives the ane^le at the . 4 <ij^e'*®^ce 

° ° ' ^ o in Angles at top 

pitch surface only. Upon looking at a small screw of ¥^^ bottom of 
coarse pitch, it will be seen that the angle at bottom 
of the thread is not so great as the angle at top of 
thread ; that is, the thread at bottom is nearer parallel 
to the center line than that at the top. 




This will be seen in Fig. 43, where A O is the center 
line ; b f shows direction of bottom of the thread, and 
d g shows direction of top of thread. The angle Kfh 
is less than the angle K g d, This difference of angle 
is due to the warped nature of a screw thread, and 
sometimes makes it necessary to change the angle for 
setting work from the figured angle, when a rotary- 
disk cutter is used, to prevent the cutter from marring 
the groove as the teeth of cutter enter and leave. 
How much to change the angle can be seen by inspec- 
tion when cutting the dummies. The change of angle 
will be more in a small gear of a given pitch than in a 
large gear of the same pitch. 

A rotary disk cutter is generally j)ref erable, because Disk-cutters, 
it cuts faster and holds its shape better. Yet it is 
hardly practical to cut low numbered pinions with 
rotary disk cutters, because for some distance below 
the pitch line the spaces are so nearly parallel. A part 
of the difficulty can be removed by making the cutter 
as small as is consistent with strength. Still more of 
the trouble can be done away with by making a cutter 
on a shank, the center of the work and the center of Shank or End 

Cutter. 

shank cutter then being in the same plane. When 
using a shank cutter the center of the work is perpen- 
dicular to the center of the cutter, no adjustment for 



98 BROWN & SHARPE MFG. CO. 

angle being made. Strictly, a shank mill does not re- 
produce its own shape in cutting a spiral groove. In 
using a shank cutter, more care is necessary to see 
that the work does not slip. It may be well to rough 
out with a disk cutter and finish with a shank cutter. 
There is not generally much difficulty in involute or 
single-curve spiral gears with disk cutters. 
caSuiSn o? ^ cylinder T diameter is to have spiral grooves 20° 
Pitch of Spiral, ^-^i^ t^^ center line of cylinder ; what will be the pitch 
of spiral? The circumference is 6.2832". The tan- 
gent of 20° is .36397. Dividing the circumference by 
the tangent of angle, we obtain ^-f||||y=17.26"-|- for 
pitch of spiral. 

Before cutting into a blank it is well to make a 
slight trace of the spiral, with the cutter, after the 
machine is geared up, to see if the gears are properly 
arranged. Attention to this may avoid spoiling a 
blank. 

The cutting of spiral gears develops some curious 
facts to one who may not have studied warped sur- 
faces. 

In the Universal Milling Machine we can cut a class 
of warped surfaces that will fit a straight edge in two 
directions. Thus, in Fig. 43, if it were possible to re- 
duce the diameter of screw and then cut the thread 
clear down to the center line A O, the bottom of the 
thread would be a straight line running through the 
center or the line A O itself. The sides would still be 
straight as in the figure. If we should cut a spiral 
groove with a plain rotary disk cutter, having parallel 
sides, the shape of the grooves would have but little 
resemblance to that of the cutter. Taking advantage 
of this principle, we learned the fact that spiral gears 
can be planed with a rack tool. 
Spiral Gears The fifcars, Fifif. 41, were planed. The tool was of 

cut with Eack , -, ,-, • i-. n -r^ -r^ * n 

Tool. the same shape as the spaces m the rack 1) D. All 

spiral gears of the same pitch could be planed with 
one tool. 

The nature of this can be seen when we consider 
that straight rack teeth can mesh with spiral gears, as 
in Fig. 40. 



PROVIDENCE, E. I. 99 

We have succeeded in cutting small spiral gears with 
a long fly tool, cutting on one side only. The shape 
of this fly tool was like a common lathe side tool. In 
this case, of course, the gears had to be reversed in 
order to finish both sides of teeth. A description and an 
illustration of cutting spiral and spur gears with a fly tool on 
our Universal Milling Machine are in the American Jfac/im- 
^si for Nov. 21, 1885. 



100 



BROWN & SHARPE MFG. CO. 



CHAPTER VI. 



HORMAL PITCH OF SPIRAL GEARS— CDRYATDRE OF PITCH 
SURFACE— FORM OF COTTERS. 



Normal to 
Curve. 



A Normal to a curve is a line perpendicular to the 
tangent at the point of tangency. 




In Fig. 44, the line B C is tangent to the arc D E F, 
and the line A E O, being perpendicular to the tan- 
gent at E, the point of tangency, is a normal to the 
arc. 

Fig. 45 is a representation of the pitch surface of a 
spiral gear. A' D' C is the circular pitch, as in Part 
I. A D C is the same circular pitch seen upon the 
periphery of a wheel. Let A D be a tooth and D C a 
space. Now, to make this space D C, the path of cut- 
ting is along the dotted line a b. By mere inspection, 
we can see that the shortest distance between two 
teeth along the pitch surface is not the distance 
ADC. 

Let the line A E B be perpendicular to the sides of 
teeth upon the pitch surface. A continuation of this 
line, perpendicular to all the teeth, is called the 
Normal Helix. The line A E B, reaching over a 
tooth and a space along the normal helix, is called the 
Normal Pitch, 



PROVIDENCE, K. I. 



101 




IFig. 4.5 



102 BROWN & SHAEPE MFG. CO. 

Normal Pitch. The Normal Pitch of a spiral gear is then : The 

shortest distance between the centers of two consecutive 

teeth measured along the pitch surface. 

In spur gears the normal pitch and circular pitch 

are alike. In the rack D D, Fig. 40, the linear pitch 

and normal pitch are alike. 

Cutter for From the foregoing it will be seen that, if we should 
Spiral Gears. 

cut the space D C with a cutter, the thickijess of which 
at the pitch line is equal to one-half the circidar pitch, 
as in spur wheels, the space would be too wide, and 
the teeth would be too thin. Hence, spiral geara 
should be cut with thinner cutters than spur gears of 
the same circular pitch. 

The angle C A B is equal to the angle of the spiral. 
The line A E B corresponds to the cosine of the angle 
CAB. Hence the rule : Multiply the cosine of angle 
To find Nor- of spiral by the circular pitch, and the product will be 
the normal pitch. One-half the normal pitch is the 
proper thickness of cutter at the pitch line. 

If the normal pitch and the angle are known Divide the 
normal pitch hy the cosine of the angle and the quotient 
will he the linear pitch. 

This may be required in a case of a spiral pinion run- 
ning in a rack. The perpendicular to the side of the rack 
is taken as the line from which to calculate angle of teeth. 
That is, this line would correspond to the axial line in spiral 
gears. This considers a rack as a gear of infinitely long 
radius ; page 12. If the condition required gives the angle 
of axis of gear and the side of the rack, we subtract the 
given angle from 90 degrees and base our caculations upon 
the remainder, which is complement of the given angle. 

The addendum and working depth of tooth should 
correspond to the normal pitch, and not to the circular 
pitch. Thus, if the normal pitch is 12 diametral, the 
addendum should be yy, the thickness .1309", and so 
on. The diameter of pitch circle of a spiral gear is 
calculated from the diametral pitch. Thus a gear of 
30 teeth 10 P would be 3" pitch diameter. 

But if the normal pitch is 12 diametral pitch, the 

blank will be Z^^" diameter instead of 3yV'- 

Normal Pitch It is evident that the normal pitch varies with the 
vanes. ^ 



PROVIDENCE, B. i. 103 

angle of spii'al. The cutter should be for the normal 
pitch. In designing spiral gears, it is well to first 
look over list of cutters on hand, and see if there are 
cutters to which the gears can be made to conform. 
This may avoid the necessity of getting a new cutter, 
or of changing both drawing and gears after they are 
under way. To do this, the problem is worked the 
reverse of the foregoing ; that is : 

First calculate to the next finer pitch cutter than To make 

■^ Angle of Spiral 

would be required for the diametral pitch. conform to Cut- 

. tera given. 

Let us take, for example, a gear 10 pitch and 30 

teeth spiral. Let the next finer cutter be for 12 pitch 

gears. The first thing is to find the angle that will 

make the normal pitch .2618", when the circular pitch 

is .3142". See table of tooth parts. This means (Fig. 

45) that the Ime A D C will be .3142" when A E B is 

.2618". Dividing .2618" by .3142" (see Chapter IV.), 

we obtain the cosine of the angle CAB, which is also 

the angle of the spii-al, ^|fi|=.833. 

The same quotient comes by dividing 10 by 12. 
^0.-833 + . Looking in the table, we find the angle 
con-esponding to the cosine .833 is 33° 30'. We now 
want to find the pitch of spiral that will give angle of 
33 J ° on the pitch surface of the wheel, 3" diameter. 
Dividing the circumference by the tangent of angle, 
we obtain the pitch of spu'al (see Chapter Y.) The 
circumference is 9.4248". The tangent of 33° 30' is 
.66188, ^^||f|^=14.23; and we have for our spiral 
14.23" lead. 

AMien the machine is not arrane-ed for the exact When exact 

. ^ Pitch cannot be 

pitch of spii'al wanted, it is generally well enough to cut. 
take the next nearest spiral. A half of an inch more 
or less in a spiral 10" pitch or more would hardly be 
noticed in angle of teeth. It is generally better to 
take the next longer spiral and cut enough deeper to 
bring center distances right. When two gears of the 
same size are in mesh with their axes parallel, a change 
of angle of teeth or spiral makes no difference in the 
correct meshing of the teeth. 

But when clears of different size are in mesh, duo Spiral Gears 

^ ofDifferenc 

regard must be had to the spirals being in pitch, pro- sizes to Mesu. 



104 



BBOWN & SHARPE MFG. CO. 



portional to their angular velocities (see Chapter V. ) 
"We come now to the curvature of cutters for spiral 
gears; that is, their shape as to whether a cutter is 
made to cut 12 teeth or 100 teeth. A cutter that is right, 
Shape of Cut- to cut a spur gear 3" diameter, may not be right for a 
spiral gear 3" diameter. To find the curvature of 
cutter, fit a templet to the blank along the line of the 
normal helix, as A E B, letting the templet reach over 
about two or three normal pitches. The curvature of 
this templet will be nearer a straight line than an arc 
of the addendum circle. Now find the diameter of a 
circle that will fit this templet, and consider this circle 
as the addendum circle of a gear for which we are to 
select a cutter, reckoning the gear as of a pitch the 
same as the normal pitch. 




Fis- 46 



Thus, in Fig. 46, suppose the templet fits a circle 
3 J" diameter, if the normal pitch is 12 to inch, dia- 
metral, the cutter required is for 12 P and 40 teeth. 
The curvature of the templet will not be quite circular, 
but is sufficiently near for practical purposes. Strictly, 
a flat templet cannot be made to coincide with the 
normal helix for any distance whatever, but any greater 
refinement than we have suggested can hardly be 
carried out in a workshop. 



PROVIDENCE, E. I. 105 

This applies more to an end cutter, for a disk cutter may 
have the right shape for a tooth space and still round off 
the teeth too much on account of the warped nature of 
the teeth. 

The difference between normal pitch and linear or 
circular pitch is plainly seen in Figs, 40 and 41. 

The rack D T>, Fig. 40, is of regular form, the depth 
of teeth being ^^ of the circular pitch, nearly (.6866 of 
the pitch, accui'ately). If a section of a tooth in either 
of the gears be made square across the tooth, that is a 
normal section , the depth of the tooth will have the 
same relation to the thickness of the tooth as in the 
rack just named. 

But the teeth of spiral gears, looking at them upon 
the side of the gears, are thicker in proportion to their 
depth, as in Fig. 41. This difference is seen between 
the teeth of the two racks D D and E E, Fig. 40. In 
the rack D D we have 20 teeth, while in the rack E E 
we have but 14 teeth ; yet each rack will run with each 
of the spiral gears A, B or C, Fig. 41, but at different 
angles. 

The teeth of one rack will accurately fit the teeth of 
the other rack face to face, but the sides of one rack 
will then be at an angle of 45° with the sides of the 
other rack. At F is a guide for holding a rack in mesh 
with a gear. 

The reason the racks will each run with either of the three 
gears is because all the gears and racks have the same normal >; 

pitch. When the spiral gears are to run together they must 
both have the same normal pitch. Hence two spiral gears 
may run correctly together though the circular pitch of one 
gear is not like the circular pitch of the other gear. 



106 BEOWN & SHARPE MFG. CO. 



CHAPTER VII. 
SCREW GEARS AND SPIRAL GEARS— GENERAL REMARKS. 



Sp^ai^Gears.*^^ ^^^ Working of Spiral gears is generally smoother 
than spur gears. A tooth does not strike along its 
whole face or length at once. Tooth contact first takes 
place at one side of the gear, passes across the face 
and ceases at the other side of the gear. This action 
tends to cover defects in shape of teeth and the adjust- 
ment of centers. 

Since the invention of machines for producing accu- 
rate epicyloidal and involute curves, it has not so often 
been found necessary to resort to spiral gears for 
smoothness of action. A greater range can be had in 
the adjustment of centers in spiral gears than in spur 
gears. The angle of the teeth should be enough, so 
that one pair of teeth will not part contact at one side 
of the gears until the next pair of teeth have met on the 
other side of the gears. When this is done the gears 
will be in mesh so long as the circumferences of their 
addendum circles intersect each other. This is some- 
times necessary in roll gears. 

Relative to spur and bevel gears in Part I., Chapter 
XII., ifc was stated that all gears finally wore them- 
selves out of shape and might become noisy. Spiral 
gears may be worn out of shape, but the smoothness 
of action can hardly be impaired so long as there are 
any teeth left. For every quantity of wear, of course, 
there will be an equal quantity of backlash, so that if 
gears have to be reversed the lost motion in spiral 
gears will be as much as in any gears, and may be 
u^n^^ShlftTof ^0^6 if there is end play of the shafts. In spiral gears 
Spiral Gears, fci^ere is end pressure upon the shafts, because of the 
screw-like action of the teeth. This end pressure is 
sometimes balanced by putting two gears upon each 
shaft, one of right and one of left hand spiral. 



PROVIDENCE, K. I. 107 

The same result is obtained in solid cast gears by 
making the pattern in two parts — one right and one 
left-hand spiral. Such gears are colloquially called 
"herring-bone gears. '^ 

In an internal spu'al gear and its pinion, the spirals 
of both wheels are either right-handed or left-handed. 
Such a combination would hardly be a mercantile 
product, although interesting as mechanical feat. 

In screw or worm-gears the axes are generally at 
right angles, or nearly so. The distinctive features of 
screw gearing may be stated as follows : 

The relative angular velocities do not depend upon 
the diameters of pitch-cylinders, as in Chapter I., 
Pai't I. Thus the worm in Chai3ter XL, Fi^. 18, can, Distinctive 

■^ ' <=* ' features of 

be any diameter — one inch or ten inches — without Screw Gearing. 

affecting the velocity of the worm-wheel. Conversely if the 

axes are not parallel we can have a pair of spiral or screw 

gears of the same diameter, but of different numbers of 

teeth. The direction in which a worm-wheel turns depends 

upon whether the worm has a right-hand or left-hand thread. 

When angles of axes of worm and worm-wheel are 

oblique, there is a practical limit to the directional 

relation of the worm-wheel. The rotation of the 

worm-wheel is made by the end movement of the 

worm-thread. 

The term worm and worm-wheel, or worm-gearing, 
is applied to cases where the worms are cut in a lathe. 

If we let two cylinders touch each other, their axes 
be at right angles, the rotation of one cylinder will 
have no tendency to turn the other cylinder, as in 
Chapter I., Part I. 

We can now see why worms and worm-wheels wear ^^'^ worm 

•^ Wheels wear 

out faster than other gearing. The length of worm- so fast. 
thi'ead, equal to more than the entire circumference of 
worm, comes in sliding contact with each tooth of the 
wheel during one turn of the wheel. 

The angle of a worm-thread can be calculated the 
same as the angle of teeth of spu'al gear. 



108 BEOWN & SHAEPE MFG. CO. 



CHAPTER VIII. 



CONTIKDED FRACTIONS— SOME APPLICATMS IM MACHIHE 
CONSTRUCTION. 



Definition of ^ continued fraction is one which has unity for its 

a Continued »' 

Fraction. numerator, and for its denominator an entire number 

l^lus a fraction, which fraction has also unity for its 
numerator, and for its denominator an entire number 
plus a fraction, and thus in order. 
The expression, L 



4 + 1 

^ is called a continued frac- 
tion. By the use of continued fractions, we are ena- 
Practicai use j^ied to find a fraction expressed in smaller numbers, 

of Continued ^ ' 

Fractions. that, for practical purposes, may be sufficiently near in 
value to another fraction expressed in large numbers. 
If we were required to cut a worm that would mesh 
with a gear 4 diametral pitch (4 P.), in a lathe having 

3 to 1-inch linear leading screw, we might, without 
continued fractions, have trouble in finding change 
gears, because the circular pitch corresponding to 

4 diametral pitch is expressed in large numbers : 

A. P— _1_8_5_4_ p' 

This example will be considered farther on. For 
illustration, we will take a simpler example. 

What fraction expressed in smaller numbers is near- 
est in value to j^jl.? Dividing the numerator and the 
denominator of a fraction by the same number does 
not change the value of the fraction. Dividing both 
con%"?nue'd terms of yVe" ^y 29, we have s^T or, what is the 
same thing expressed as a continued fraction, 5-t-_i_. The 
continued fraction 5+X is exactly equal to -f^j. If 
now, we reject the -^j, the fraction -| will be larger 
than 6+ 1 , because the denominator has been dimin- 
ished, 5 being less than 6^\. | is something near 
^2^_ expressed in smaller numbers than 29 for a 



PROVIDENCE, E. I. 109 

numerator and 146 for a denominator. Reducing ^ 
and y2j9g. to a common denominator, we have ^=^|^ 
^^^ fA— TTo- Subtracting one from tlie other, we 
have y^-Q, which is the difference between ^ and -^^, 
Thus, in thinking of y^g- as ^, we have a pretty fair 
idea of its vahie. 

There are fourteen fractions with terms smaller than 
29 and 146, which are nearer -ffj than \ is, such as 
■fl, ^{ and so on to f^j. In this case by continued frac- 
tions we obtain only one approximation, namely -J^, and 
any other approximations, as ^f, -Jf-, &c., we find by 
trial. It will be noted that all these approximations 
are greater in value than ^iV. There are cases, how- 
ever, in which we can, by continued fractions, obtain 
approximations both greater and less than the required 
fraction, and these^ill be the nearest possible approxi- 
mations that there can be in smaller terms than the 
given fraction. 

In the French metric system, a millimetre is equal 
to .03937 inch; what fraction in smaller terms ex- 
presses .03937" nearly? .03937, in a vulgar fraction, 
^s T o 00 00 - Dividing both numerator and denominator 
by 3937, we have 25 1 sts . Rejecting from the de- 
nominator of the new fraction, HH, the fraction -^\ 
gives us a pretty good idea of the value of .03937". 
If in the expression, "25+1111, we divide both terms of 
the fraction ^^ by 1575, the value will not be changed. 
Performing the division, we have 1 . 

° 25 + 1 



2 + 787 
1575- 

We can now divide both terms of ^-^\ by 787, 
without changing its value, and then substitute the 
new fraction for ^Wt ^^ ^^® continued fraction. 

Dividing again, and substituting, we have : 
1 

25 +J^ 

2 + 1 

2+J_ 
787 

as the continued fraction that is exactly equal to 
.03937. 



110 BROWN & SHARPE MFG. CO. 

In performing the divisions, the work stands thus 

3937) 100000 (25 

7874 



19685 
1575) 3937 - 
3150 



787) 1575 (2 
1574 



1) 787 (787 
787 
•0- 

That is, dividing the last divisor by the last remain- 
der, as in finding the greatest common divisor. The 
quotients become the denominators of the continued 
fraction, with unity for numerators. The denominators 
25, 2, and so on, are called incomplete quotients, since 
they are only the entire parts of each quotient. The 
first expression in the continued fraction is -^^ or 
.04— a little larger than .03937. If, now, we take 
25-qri) we shall come still nearer .03937. The expres- 
sion as-qrr is merely stating that 1 is to be divided by 
1h\. To divide, we first reduce 25J to an improper 
fraction, ^, and the expression becomes IT, or one 

divided by ^. To divide by a fraction, "Invert the 
divisor, and proceed as in multiplication." We 
then have -^\ as the next nearest fraction to .03937. 
^2j-=i.0392 + , which is smaller than .03937. To get still 
nearer, we take in the next part of the continued frac- 
tion, and have 1 



25 + 1 



2 + 1 
2- 

We can bring the value of this expression into a 
fraction, with only one number for its numerator and 
one number for its denominator, by performing the 
operations indicated, step by step, commencing at the 
last part of the continued fraction. Thus, 2-f-^, or 
2J, is equal to |, Stopping here, the continued frac- 
tion would become i 

25-fJ_ 
_5 
2- 

1 J^ 

Now, ^ equals |, and we have 25 -\-^, 25f equals 

2 5 

-J|-i; substituting again, we have li^. Dividing 1 by 

-1^^, we have y|T^. yfy is the nearest^ fraction to 



PEOYIDENCE, E. I. Ill 

.03937, unless we reduce the whole continued fraction 
1 

S5 4-1 

2 + 1 

2 + ^, which would give us back the .03987 itself. 

y|y=:. 03937007, which is only ^^-^i^^ larger 
.03937. It is not often that an approximation will 
come so near as this. 

This ratio, 5 to 127, is used in cutting millimeter Practical use 

.1 -1 T<. .1 1 T <! j^i 1 ii . of the foregoing 

thread screws. If the leading screw of the lathe is Example. 
1 to one inch, the cliange gears will have the ratio of 
5 to 127 j if 8 to one inch, the ratio will be 8 times 
as large, or 40 to 127; so that with leading screw 8 to 
inch, and change gears 40 and 127, we can cut milli- 
meter threads near enough for practical purposes. 

The foregoing operations are more tedious in de- 
scription than in use. The steps have been carefully 
noted, so that the reason for each step can be seen 
from rules of common arithmetic, the operations being 
merely reducing complex fractions. The reductions, 
"sV' "A:» tIt' ®^^-' ^^® called convergents, because they 
come nearer and neai'er to the required .03937. The 
operations can be shortened as follows: 

Let us find the fractions converging towards .7854", ^^^°^p^®- 
the circular pitch of 4 diametral pitch, .1%^^=^-^-^-^-^; 
reducing to lowest terms, we have ff|-J. Applying 
the operation for the greatest common divisor: 

3927) 5000 (1 
3927 

1073) 3927 (3 
3219 
708) 1073 (1 
708 

365) 708 (1 
365 

343) 365 (1 
343 

22) 343 (15 
22^ 
123 
110 

13) 22 (1 
13 



9) 13 (1 



4)9(2 
8 

"l) 4 (4 
4 




Bringing the various incomplete quotients as de- 
nominators in a continued fraction as before, we have : 



112 BEOWN & SHAKPE MFG. CO. 

1 

1 + 1 

. 3 + 1 

1+JL 

1 + 1 

1 + 1 

15 + 1 

1 + 1 

1+L 

' 2 + :^ 

Now arrange eacli partial quotient in a line, thus : 

13111 15 11 2 4 

1 f t i ii HI iff m tVsV nu 

Now place under the first incomplete quotient the 
first reduction or convergent ^, which, of course, is 1 ; 
put under the next partial quotient the next reduction or 
convergent j^p or ji, which becomes f . 

1 is larger than .7854, and f is less than .7854. 

Having made two reductions, as previously shown, 
we can shorten the operations by the following rule for next 
convergents : Multiply the numerator of the convergent 
just found by the denominator of the next term, of the con- 
tinued fraction^ or the next incomplete quotient^ and add 
to the product the numerator of the p)receding convergent ; 
the sum tvill be the numerator of the next convergent. 

Proceed in the same way for the denominator. 
Continue until the last convergent is the original frac- 
tion. Under each incomplete quotient or denominator 
from the continued fraction arranged in line, will be 
seen the corresponding convergent or reduction. The 
convergent ^^ is the one commonly used in cutting 
racks 4 P. This is the same as calling the circumference of 
a circle 22-7 when the diameter is one (1) ; this is also the 
common ratio for cutting any rack. The equivalent decimal 
to ij is .7857 X , being about Yofoo- large. In three set- 
tings for rack teeth, this error would amount to about .001" 

For a worm, this corresponds to ^j- threads to 1" ; 
now, with a leading screw of lathe 3 to V\ we would 
want gears on the spindle and screw in a ratio of 33 
to 14. 

Hence, a gear on the spindle with 66 teeth, and a 
gear on the 3 thread screw of 28 teeth, would enable 
us to cut a worm to fit a 4 P gear. 



PROVIDENCE, R. I. 



113 



CHAPTER IX. 
ANGLE OF PRESSURE 



In Fig. 47, let A be any flat disk lying upon a hori- 
zontal plane. Take any piece, B, witli a square end, 
a b. Press against A with the piece B in the direction 
of the arrow. 





Fig. 4T 



Fig. 48 



It is evident A will tend to move directly ahead of 
B in the normal line c d. Now (Fig. 48) let the piece 
B, at one corner/*, touch the piece A. Move the piece 
B along the line d e, in the direction of the arrow. 

It is evident that A will not now tend to move in 
the line d e, but will tend to move in the direction of 
the normal c d. When one piece, not attached, presses 
against another, the tendency to move the second 
piece is in the direction of the normal, at the point of 
contact. This normal is called the line of pressure. LineofPress- 
The angle that this line makes with the path of the 
impelling piece, is called the a^igle of pressure. 

In Part I., Chapter IV., the lines B A and B A' are 
called lines of pressure. This means that if the gear 



114 BROWN & SHARPE MFG. CO. 

drives the rack, the tendency to move the rack is not 
in the direction of pitch line of rack, but either in the 
direction B A or B A', as we turn the wheel to the left 
or to the right. 

The same law holds if the rack is moved in the 
direction of the pitch line; the tendency to move the 
wheel is not directly tangent to the pitch circle, as if 
driven by a belt, but in the direction of the line of 
pressure. Of course the rack and wheel do move in 
the paths prescribed by their connections with the 
framework, the wheel turning about its axis and the 
rack moving along its ways. This pressure, not in a 
direct path of the moving piece, causes extra friction 
in all toothed gearing that cannot well be avoided. 

Although this pressure works out by the diagram, 
as we have shown, yet, in the actual gears, it is not at 
all certain that they will follow the law as stated, 
because of the friction of teeth among themselves. If 
the driver in a train of gears has no bearing upon its 
tooth-flank, we apprehend there will be but little 
tendency to press the shafts apart. 
Arc of Action. rjij^^ ^^^ through which a wheel passes while one of 

its teeth is in contact is called the arc of action. 
tenf^of^^in^erl Until within a few years, the base of a system of 
^^^^^g^^^i® double-curve interchangeable gears was 12 teeth. It 
is now 15 teeth in the best practice (see Chapter VII., 
Part I.) 

The reason for this change was : the base, 15 teeth, 
gives less angle of pressure and longer arc of contact, 
and hence longer lifetime of gears. 



PROVIDENCE, R. T. US 



CHAPTER X. 
I8TERNAL GEARS 



In Part I., Chapter YIII., it was stated that the 
space of an internal gear is the same as the tooth of a 
spur gear. This applies to involute or single-curve 
gears as well as to double-curve gears. 

The sides of teeth in involute internal gears will be 
hollowing. It, however, has been customary to cut 
internal gears with spur gear-cutters, a No. 1 cutter 
generally being used. This makes the teeth sides 
convex. Special cutters should be made for coarse Special Cut, 

.,,-,, TT''«i 1 t6^8 for coarse 

pitch double-curve gears. In designmg internal gears, Pitch. 

it is sometimes necessary to depart from the system 
with 15-tooth base, so as to have the pinion differ from 
the wheel by less than 15 teeth. The rules given in 
Part I., Chapters YII. and YIII., will apply in making 
gears on any base besides 15 teeth. If the base is 
low-numbered and the pinion is small, it may be neces- 
sary to resort to the method given at the end of Chap- 
ter YII., because the teeth may be too much rounded 
at the points by following the approximate rules. 
The base must be as small as the diiference between Base for in- 

. . . ~1 ternal Gear 

the internal gear and its pinion. The base can be Teeth, 
smaller if desired. 

Let it be required to make an internal gear, and 
pinion 24 and 18 teeth, 3 P. Here the base cannot 
be more than 6 teeth. 

In Fig. 49 the base is 6 teeth. The arcs A K and 
O k, drawn about T, have a radius equal to the radius 
of the pitch circle of a 6-tooth gear, 3 P, instead of a 
15-tooth gear, as in Chapter YIII., Part I. 

The outline of teeth of both gears and pinion is ypescriptiou of 
made similar to the gear in Chapter YIII. The same 



116 



BROWN & SHARPE MFG. CO. 



A 






V 



X 



GEAR, 24 TEETH. 
PINION, 18 TEETH, 3 P. 

P = 3 

N =24 and 18 
P'= 1.0472' 
t^ 5236" 
S=. .3333' 
0"^= .6666' 
S+/= .3857' 
P"+/« .7190' 



C 



INTERNAL GEAR AND PINION IN MESH, 



PROVIDENCE, E. I. 117 

letters refer to similai' parts. The clearance circle is, 
however, di'awn on the outside for the internal gear. 
As before stated, the spaces of a spur w^heel become 
the teeth of an internal wheel. The teeth of internal 
gears require but little for fillets at the roots ; they 
are generally strong enough without fillets. The 
teeth of the pinion are also similar to the gear in 
Chapter VIII., substituting 6-tooth for 15-tooth base. 
To avoid confusion, it is well to make a complete 
sketch of one gear before making the other. The arc 
of action is longer in internal gears than in external 
geai's. This property sometimes makes it necessary 
to give less fillets than in external gears. 

In Fig. 49 the angle K T A is 30° instead of 12°, as 
in Fig. 12. This brings the line of pressure L P at 
an angle of 60° with the radius C T, instead of 78°. 
A system of spur gears could be made upon this 
6-tooth base. These gears would interchange, but no 
gear of this 6-tooth system would mesh with a double- 
curve gear made upon the 15-tooth system in Part 1. 

The "Willis" double-cui've Odontograph is based ^ Base of wiiiis 

° ^ Odontograph. 

upon radial flank gears of 12 teeth this makes the angle 

of pressure 75 in the Willis system, when the teeth are in 

contact at the common point of the pitch circle. 



118 



BROWN & SHARPE MFG. CO. 



CHAPTER XL 



STRENGTH OF GEARING. 



On this subject we cannot give any definite rule derived . 
from our own experience, but refer those interested to 
Cooper's collection of 24 rules from different writers in the 
"Journal of the Franklin Institute" for July, 1879. 

We give a few examples of average breaking strain of our 
Combination Gears, as determined by dynamometer, 
the pressure being measured at the pitch line. These 
gears are of cast iron, with cut teeth. 



DIAMETRAL PITCH. 



10 

8 
6 
5 



1 1-16 
1 1-4 
1 9-16 

1 7-8 



No. TEETH. 


Revolutions 
Per Minute. 


Pressure at 
Pitch Line. 


110 


27 


1060 


72 


40 


1460 


72 


27 


2220 


90 


18 


2470 



These are the actual pressures for the particular 
widths given. 

If we take a safe pressure at 1-3 of the foregoing break- 
ing strain, we shall have for 



10 Pitch 353 1-3 Lbs. at the Pitch Line. 
8 " 486 2-3 " " 

6 " 740 " " 

5 " 823 1-3 " " 

The width of the face of a gear is in good proportion 
when it is 2| times the circular pitch. Brown & 
Sharpe's rule is, width ^|+.25" 



PROVIDENCE, R. I. 



119 



TABLE OF DECIMAL EQUIVALENT 



OF MILLIMETERS AND FRACTIONS OF MILLIMETERS. 



mm. Inches. 


mm. Inches. 


mm. 


Inches. 


^V=. 00079 


|1=. 02047 


2= 


.07874 


-^%=. 00157 


If =.02126 


.3= 


.11811 


■A^=. 00236 


If =.02205 


4= 


.15748 


-/o = . 00315 


If =.02283 


5= 


.19685 


^=.00394 


If =.02362 


6= 


.23622 


■/o = . 00472 


If =.02441 


7= 


.27559 


^V^. 00551 


If =.02520 


8= 


.31496 


•i^=. 00630 


If =.02598 


9= 


.35433 


^=.00709 


If =.02677 


10= 


.39370 


i^=. 00787 


If =.02756 


11= 


.43307 


|i=. 00866 


If =.02835 


12= 


.47244 


M=. 00945 


If =.02913 


13= 


.51181 


if-. 01024 


If =.02992 


14= 


.55118 


iA=. 01102 


If =.03071 


15= 


.59055 


i|=. 01181 


if =.03150 


16= 


.62992 


i|=. 01260 


If =.03228 


17= 


.66929 


if = . 01339 


tf=. 03307 


18= 


.70866 


it=. 01417 


tf=. 03386 


19= 


.74803 


if =.01496 


If =.03465 


20= 


.78740 


|^=. 01575 


If =.03543 


21 = 


.82677 


!-; = . 01654 


If =.03622 


22= 


.86614 


If =.01732 


If =.03701 


23= 


.90551 


If =.01811 


If =.03780 


24= 


.94488 


If =.01890 


if =.03858 


25= 


.98425 


If =.01969 


1=. 03937 


26=1 


.02362 



10 mm. = l Centimeter= 0.3937 inches. 
10 cm. =1 Decimeter =3.937 
10 dm. =1 Meter =39.37 " 

25.4 mm.=l English Inch. 



120 



BBOWN & SHAEPE MFG. CO. 



NATURAL SINE. 



Deg. 


0' 


10' 


20' 


30' 


40' 


50' 


60' 







.00000 


.00291 


.00581 


.00872 


.01163 


.01454 


.01745 


89 


1 


.01745 


.02036 


.02326 


.02617 


.02908 


.03199 


.03489 


88 


3 


.03489 


.03780 


.04071 


.04361 


.04652 


.04943 


.05233 


87 


3 


.05233 


.05524 


.05814 


.06104 


.06395 


.06685 


.06975 


86 


4 


.06975 


.07265 


.07555 


.07845 


.08135 


.08425 


.08715 


85 


5 


.08715 


.09005 


.09295 


.09584 


.09874 


.10163 


.10452 


84 


6 


.10452 


.10742 


.11031 


.11320 


.11609 


.11898 


.12186 


83 


7 


.12186 


.12475 


.12764 


.13052 


.13341 


. 13629 


.13917 


82 


8 


.13917 


.14205 


.14493 


.14780 


.15068 


.15356 


.15643 


81 


9 


.15643 


.15930 


.16217 


.16504 


.16791 


.17078 


.17364 


80 


10 


.17364 


.17651 


.17937 


.18223 


.18509 


.18795 


.19080 


79 


11 


.19080 


.19366 


.19651 


.19936 


.20221 


.20506 


.20791 


78 


12 


.20791 


.21075 


.21359 


.21644 


.21927 


.22211 


.22495 


77 


13 


.22495 


.22778 


.23061 


.23344 


.23627 


.23909 


.24192 


76 


14 


.24192 


.24474 


.24756 


.25038 


.25319 


.25600 


.25881 


75 


15 


.25881 


.26162 


.26443 


.26723 


.27004 


.27284 


.27563 


74 


16 


.27563 


.27843 


.28122 


.28401 


.28680 


.28958 


.29237 


73 


17 


.29237 


.29515 


.29793 


.30070 


.30347 


.30624 


.30901 


72 


18 


.30901 


.31178 


.31454 


.31730 


.32006 


.32281 


.32556 


71 


19 


.32556 


.32831 


.33106 


.33380 


.33654 


.33928 


.34202 


70 


20 


.34202 


.34475 


.34748 


.35020 


.35293 


.35565 


.35836 


69 


21 


.35836 


.36108 


.36379 


.36650 


.36920 


.37190 


.37460 


68 


22 


.37460 


.37730 


.37999 


.38268 


.38536 


.38805 


.39073 


67 


23 


.39073 


.39340 


.39607 


.39874 


.40141 


.40407 


.40673 


66 


24 


.40673 


.40939 


.41204 


.41469 


.41733 


.41998 


.42261 


65 


25 


.42261 


.42525 


.42788 


.43051 


.43313 


.43575 


.43837 


64 


26 


.43837 


.44098 


.44359 


.44619 


.44879 


.45139 


.45399 


63 


27 


.45399 


.45658 


.45916 


.46174 


.46432 


.46690 


.46947 


62 


28 


.46947 


.47203 


.47460 


.47715 


.47971 


.48226 


.48481 


61 


29 


.48481 


.48735 


.48989 


.49242 


.49495 


. 49747 


.50000 


60 


30 


.50000 


.50251 


.50503 


.50753 


.51004 


.51254 


.51503 


59 


31 


.51503 


.51752 


.52001 


.52249 


.52497 


.52745 


.52991 


58 


32 


.52991 


.53238 


.53484 


.53730 


.53975 


.54219 


.54463 


57 


33 


.54463 


.54707 


.54950 


.55193 


.55436 


.55677 


.55919 


56 


34 


.55919 


.56160 


.56400 


.56640 


.56880 


.57119 


.57357 


55 


35 


.57357 


.57595 


.57833 


.58070 


.58306 


.58542 


.58778 


54 


36 


.58778 


.59013 


.59248 


.59482 


.59715 


.59948 


.60181 


53 


37 


.60181 


.60413 


.60645 


.60876 


.61106 


.61336 


.61566 


52 


38 


.61566 


.61795 


.62023 


.62251 


.62478 


.62705 


.62932 


51 


39 


.62932 


.63157 


.63383 


.63607 


.63832 


.64055 


.64278 


50 


40 


.64278 


.64501 


.64723 


.64944 


.65165 


.65386 


.65605 


49 


41 


.65605 


.65825 


.66043 


.66262 


.66479 


.66696 


.66913 


48 


42 


.66913 


.67128 


.67344 


.67559 


.67773 


.67986 


.68199 


47 


43 


.68199 


.68412 


.68624 


.68835 


.69046 


.69256 


.69465 


46 


44 


.69465 


.69674 


.69883 


.70090 


.70298 


.70504 


.70710 


45 


- 


60' 


50' 


40' 


30' 


20' • 


10' 


C 


Deg. 



NATURAL COSINE. 



PEOVIDENCE, K. I. 



121 



NATURAL SINE. 



Deg. 


^' 


10' 


20' 


30' 


I 

40' 


50' 


60' 




45 


.70710 


! .70916 


.71120 


.71325 


.71538 


.71731 


.71934 


44 


46 


.71934 


1 .72135 


.72336 


.72537 


.72787 


.72936 


.73135 


48 


47 


.73185 


.73333 


. 73530 


.73727 


.73928 


.74119 


.74314 


42 


48 


.74314 


.74508 


.74702 


.74895 


.75088 


. 75279 


.75471 


41 


49 


.75471 


.75661 


.75851 


.76040 


.76229 


.76417 


.76604 


40 


50 


.76604 


.76791 


.76977 


.77102 


.77847 


.77581 


.77714 


39 


51 


.77714 


.77897 


. 78079 


.78260 


.78441 


.78621 


.78801 


38 


53 


.78801 


.78979 


.79157 


.79335 


. 79513 


.79688 


.79863 


37 


53 


.79863 


.80038 


.80212 


.80385 


.80558 


.80730 


.80901 


36 


54 


.80901 


.81072 


.81242 


.81411 


.81580 


.81748 


.81915 


35 


55 


.81915 


.82081 


.82247 


.82412 


.83577 


.83740 


.82903 


34 


56 


.82903 


.83066 


.83227 


.83388 


.83548 


.83708 


.83867 


33 


57 


.83867. 


.84025 


.84182 


.84339 


.84495 


.84650 


.84804 


32 


58 


.84804 


.84958 


.85111 


.85264 


.85415 


.85566 


.85716 


31 


59 


.85716 


.85866 


.86014 


.86162 


.86810 


.86456 


.86602 


30 


60 


.86602 


.86747 


.86892 


.87035 


.87178 


.87330 


.87462 


29 


61 


.87462 


.87603 


.87742 


.87881 


.88030 


.88157 


.88294 


28 


63 


.88294 


.88430 


.88566 


.88701 


.88835 


.88968 


.89100 


27 


63 


.89100 


.89232 


.89363 


.89493 


.89622 


.89751 


.89879 


26 


64 i 


.89879 


.90006 


.90132 


.90258 


.90383 


.90507 


.90680 


25 


65 i 


.90630 


.90753 


.90875 


.90996 


.91116 


.91285 


.91354 


24 


66 


.91354 


.91472 


.91589 


.91706 


.91821 


.91936 


.92050 


23 


67 


.92050 


.93163 


.92276 


.92388 


.92498 


.92609 


.93718 


22 


68 


.92718 


.92827 


.92934 


.93041 


.98148 


.98253 


.93358 


21 


69 


.93358 


.93461 


.93565 


.93667 


.93768 


.93869 


.93969 


20 


70 ! 


.93969 


.94068 


.94166 


.94264 


.94360 


.94456 


.94551 


19 


71 j 


.94551 


.94646 


.94789 


.94832 


.94924 


.95015 


.95105 


18 


73 i 


.95105 


.95195 


.95288 


.95371 


.95458 


.95545 


.95630 


17 


73 1 


.95630 


.95715 


.95799 


.95882 


.95964 


.96045 


.96126 


16 


74 I 


.96126 


.96205 


.96284 


.96863 


.96440 


.96516 


.96592 


15 


75 1 


.96592 


.96667 


.96741 


.96814 


.96887 


.96958 


.97029 


14 


76 1 


.97029 


.97099 


.97168 


.97337 


.97304 


.97371 


.97437 


13 


77 1 


.97437 


.97502 


.97566 


.97631) 


.97692 


.97753 


.97814 


12 


78 


.97814 


.97874 


.97934 


.97993 


.98050 


.98106 


.98162 


11 


79 


.98162 


.98217 


.98272 


.98835 


.98878 


.98439 


.98480 


10 


80 ! 


.98480 


.98530 


.98580 


.98628 


.98676 


. 98733 


.98768 


9 


81 1 


.98768 


.98813 


.98858 


.98901 


.98944 


.98985 


.99026 


8 


82 1 


.99026 


.99066 


.09106 


.99144 


.99182 


.99318 


.99254 


7 


83 


.99254 


.99289 


.99323 


.99857 


.99889 


.99431 


.99452 


6 


84 : 


.99452 


.99482 


.99511 


.99589 


.99567 


.99593 


.99619 


5 


85 ' 


.99619 


.99644 


.99668 


.99691 


.99714 


. 99785 


. 99756 


4 


86 ! 


.99756 


.99776 


.99795 


. 99813 


.99880 


.99847 


.99863 


3 


87 1 


.99863 


.99877 


.99891 


.99904 


.99917 


.99928 


.99939 


2 


88 ; 


.99939 


.99948 


.99957 


.99965 


.99972 


.99979 


.99984 


1 


89 


.99984 


.99989 


.99993 


.99996 


.99998 


.99999 


1.0000 





~ 


60' 

i 


50' 


40' ! 


W 


20' 


10' 


0' 


Deg. 



NATURAL COSINE. 



122 



BROWN & SHARPE MFG. CO. 



NATUKAL TANGENT. 



Deg. 


0' 


10' 


20' 


30' 


40' 


50' 


60' 







.00000 


.00290 


.00581 


.00872 


.01168 


.01454 


.01745 


89 


1 


.01745 


.02036 


.02327 


.02618 


.02909 


.03200 


.03492 


88 


2 


.03492 


.03783 


.04074 


.04366 


.04657 


.04949 


.05240 


87 


3 


.05240 


.05532 


.05824 


.06116 


.06408 


.06700 


.06992 


86 


4 


.06992 


.07285 


.07577 


.07870 


.08162 


.08455 


.08748 


85 


5 


.08748 


.09042 


.09335 


.09628 


.09922 


.10216 


.10510 


84 


6 


.10510 


.10804 


.11099 


.11393 


.11688 


.11983 


.12278 


83 


7 


.12278 


.12573 


.12869 


.18165 


.13461 


.13757 


.14054 


82 


8 


.14054 


.14350 


.14647 


.14945 


.15242 


.15540 


.15888 


81 


9 


.15838 


.16136 


.16485 


.16784 


.17033 


.17332 


.17682 


80 


10 


.17632 


.17932 


.18238 


.18588 


.18834 


.19136 


.19438 


79 


11 


.19438 


. 19740 


.20042 


.20845 


.20648 


.20951 


.21255 


78 


12 


.21255 


.21559 


.21864 


.22169 


.22474 


.22780 


.23086 


77 


13 


.23086 


.23393 


.23700 


.24007 


.24315 


.24624 


.24932 


76 


14 


.24932 


.25242 


.25551 


.25861 


.26172 


.26483 


.26794 


75 


15 


.26794 


.27106 


.27419 


.27732 


.28046 


.28360 


.28674 


74 


16 


.28674 


.28989 


.29805 


.29621 


.29938 


.30255 


.30578 


73 


17 


.30573 


.3089L 


.31210 


.31529 


.31850 


.32170 


.32492 


72 


18 


.32492 


.32813 


.33186 


.33459 


.33788 


.84107 


.84482 


71 


19 


.34432 


.34758 


.35084 


.85411 


.85739 


.36067 


.86397 


70 


20 


.36397 


.36726 


.37057 


.37888 


.37720 


.38053 


.38886 


69 


21 


.38386 


.38720 


.39055 


.39391 


.39727 


.40064 


.40402 


68 


22 


.40402 


.40741 


.41080 


.41421 


.41762 


.42104 


.42447 


67 


23 


.42447 


.42791 


.43135 


.43481 


.48827 


.44174 


.44522 


66 


24 


.44522 


.44871 


.45221 


.45572 


.45924 


.46277 


.46630 


65 


25 


.46630 


.46985 


.47841 


.47697 


.48055 


.48413 


.48773 


64 


26 


.48773 


.49133 


.49495 


.49858 


.50221 


.50586 


.50952 


63 


27 


.50952 


.51319 


.51687 


.52056 


.52427 


.52798 


.53170 


62 


28 


.53170 


.53544 


.58919 


.54295 


.54672 


.55051 


.55430 


61 


29 


.55430 


.55811 


.56198 


.56577 


.56961 


.57347 


.57735 


60 


30 


.57735 


.58123 


.58513 


.58904 


.59297 


.59690 


.60086 


59 


81 


.60086 


.60482 


.60880 


.61280 


.61680 


.62083 


.62486 


58 


32 


.62486 


.62892 


.63298 


.63707 


.64116 


.64528 


.64940 


57 


33 


.64940 


.65355 


.65771 


.66188 


.66607 


.67028 


.67450 


56 


34 


.67450 


.67874 


.68300 


.68728 


.69157 


.69588 


.70020 


55 


35 


.70020 


.70455 


.70891 


.71329 


.71769 


.72210 


.72654 


54 


36 


.72654 


.73099 


.73546 


.73996 


.74447 


.74900 


. 75355 


53 


37 


.75355 


.75812 


.76271 


.76732 


.77195 


.77661 


.78128 


52 


38 


.78128 


.78598 


.79069 


.79543 


.80019 


.80497 


. 80978 


51 


39 


.80978 


.81461 


.81940 


.82433 


.82923 


.83415 


.83910 


50 


40 


.83910 


.84406 


.84900 


.85408 


.85912 


.86419 


.86928 


49 


41 


.86928 


.87440 


.87955 


.88472 


.88992 


.89515 


.90040 


48 


42 


.90040 


.90568 


.91099 


.91633 


.92169 


.92709 


.93251 


47 


43 


.93251 


.93796 


.94845 


.94896 


.95450 


.96008 


.96568 


46 


44 


.96568 


.97132 


.97699 


.98269 


.98848 


.99419 


1.0000 


45 




60' 


50' 


40' 


30' 


20' 


10' 


0' 


Deg. 



NATUEAL COTANGENT. 



PROVIDENCE, 3. I, 



123 



NATURAL TANGENT. 



Deg. 


0' 


10' 


20' 


30' 


40' 


50' 


60 




45 


1.0000 


1.0058 


1.0117 


1.0176 


1.0235 


1.0295 


1.0355 


44 


46 


1.0355 


1.0415 


1.0476 


1.0537 


1.0599 


1.0661 


1.0723 


43 


47 


1.0723 


1.0786 


1.0849 


1.0913 


1.0977 


1 . 1041 


1.1106 


42 


48 


1.1106 


1.1171 


1.1236 


1.1302 


1.1369 


1.1436 


1.1503 


41 


49 


1.1503 


1.1571 


1.1639 


1.1708 


1.1777 


1.1847 


1.1917 


40 


50 


1.1917 


1.1988 


1.2059 


1.2131 


1.2203 


1.2275 


1.2349 


39 


51 


1.2349 


1.2422 


1.2496 


1.2571 


1.2647 


1.2723 


1.2799 


38 


52 


1.2799 


1.2876 


1.2954 


1.3032 


1.3111 


1.3190 


1.3270 


37 


53 


1.3270 


1.3351 


1.3432 


1.3514 


1.3596 


1.3680 


1.3763 


36 


54 


1.3763 


1.3848 


1.3933 


1.4019 


1.4106 


1.4193 


1.4281 


35 


55 


1.4281 


1.4370 


1.4459 


1.4550 


1.4641 


1.4733 


1.4825 


34 


56 


1.4825 


1.4919 


1.5013 


1.5108 


1.5204 


1.5301 


1.5398 


33 


57 


1.5398 


1.5497 


1.5596 


1.5696 


1.5798 


1.5900 


1.6003 


32 


58 


1.6003 


1.6107 


1.6212 


1.6318 


1.6425 


1.6533 


1.6642 


31 


59 


1.6642 


1.6753 


1.6864 


1.6976 


1.7090 


1.7204 


1.7320 


30 


60 


1.7320 


1.7437 


1.7555 


1.7674 


1.7795 


1.7917 


1.8040 


29 


61 


1.8040 


1.8164 


1.8290 


1.8417 


1.8546 


1.8676 


1.8807 


28 


63 


1.8807 


1.8940 


1.9074 


1.9209 


1.9347 


1.9485 


1.9626 


27 


63 


1.9626 


1.9768 


1.9911 


2.0056 


2.0203 


2.0352 


2.0503 


26 


64 


3.0503 


2.0655 


2.0809 


2.0965 


2.1123 


2.1283 


2.1445 


25 


65 


2.1445 


2.1609 


2.1774 


2.1943 


2.2113 


2.2285 


2.2460 


24 


66 


2.2460 


2.2637 


2.2816 


2.2998 


2.3182 


2.3369 


2.3558 


23 


67 


2.3558 


2.3750 


2.3944 


2.4142 


2.4342 


2.4545 


2.4750 


22 


68 


2.4750 


2.4959 


2.5171 


2.5386 


2.5604 


2.5826 


2.6050 


21 


69 


2.6050 


2.6279 


2.6510 


2.6746 


2.6985 


2.7228 


2.7474 


20 


70 


2.7474 


2.7725 


2.7980 


2.8239 


2.8502 


2.8770 


2.9042 


19 


71 


2.9042 


2.9318 


2.9600 


2.9886 


3.0178 


3.0474 


3.0776 


18 


72 


3.0776 


3.1084 


3.1397 


3.1715 


3.2040 


3.2371 


3.2708 


17 


73 


3.2708 


3.3052 


3.3402 


3.3759 


3.4123 


3.4495 


3.4874 


16 


74 


3.4874 


3.5260 


3.5655 


3.6058 


3.6470 


3.6890 


3.7320 


15 


75 


3.7320 


3.7759 


3.8208 


3.8667 


3.9136 


3.9616 


4.0107 


14 


76 


4.0107 


4.0610 


4.1125 


4.1653 


4.2193 


4.2747 


4.3314 


13 


77 


4.3314 


4.3896 


4.4494 


4.5107 


4.5736 


4.6382 


4.7046 


12 


78 


4.7046 


4.7728 


4.8430 


4.9151 


4.9894 


5.0658 


5.1445 


11 


79 


5.1445 


5.2256 


5.3092 


5.3955 


5.4845 


5.5763 


5.6712 


10 


80 


5.6712 


5.7693 


5.8708 


5.9757 


6.0844 


6.1970 


6.3137 


9 


81 


6.3137 


6.4348 


6.5605 


6.6911 


6.8269 


6.9682 


7.1153 


8 


82 


7.1153 


7.2687 


7.4287 


7.5057 


7.7703 


7.9530 


8.1443 


7 


83 


8.1443 


8.3449 


8.5555 


8.7768 


9.0098 


9.2553 


9.5143 


6 


84 


9.5143 


9.7881 


10.078 


10.385 


10.711 


11.059 


11.430 


5 


85 


11.430 


11.826 


12.250 


12.706 


13.196 


13.726 


14.300 


4 


86 


14.300 


14.924 


15.604 


16.349 


17.169 


18.075 


19.081 


3 


87 


19.081 


20.205 


21.470 


22.904 


24.541 


26.431 


28.636 


2 


88 


28.636 


31.241 


34.367 


38.188 


42.964 


49.103 


57.290 


1 


89 


57.290 


68.750 


85.939 


114.58 


171.88 


343.77 


GO 







60' 


50' 


40' 


30' 


20' 


10' 


0' 


Deg. 

t 



NATURAL COTANGENT. 



124 



BBOWN & SHAEPE MFG. CO. 



NATUKAL SECANT. 



i 
Deg. 


0' 


10' 


20' 


30' 


47 


50 


60' 







1.0000 


1.0000 


1.0000 


1.0000 


1.0000 


1.0001 


1.0001 


89 


1 


l.OOOl 


1.0002 


1.0002 


1.0003 


1.0004 


1.0005 


1.0006 


88 


2 


1.0006 


1.0007 


1.0008 


1.0009 


1.0010 


1.0012 


1.0013 


87 


3 


1.0013 


1.0015 


1.0016 


1.0018 


1.0020 


1.0022 


1.0024 


86 


4 


1.0024 


1.0023 


1.0028 


1.0030 


1.0033 


1.0035 


1.0038 


85 


5 


1.0038 


1.0040 


1.0043 


1.0046 


1.0049 


1.0052 


1.0055 


84 


6 


1.0055 


1.0058 


1.0031 


1.0064 


1.0068 


1.0071 


1.0075 


83 


7 


1.0075 


1.0078 


1.0082 


1.0086 


1.0090 


1.0094 


1.0098 


82 


8 


1.0098 


1.0102 


1.0103 


1.0111 


1.0115 


1.0120 


1.0124 


81 


9 


1.0124 


1.0129 


1.0134 


1.0139 


1.0144 


1.0149 


1.0154 


80 


10 


1.0154 


1.0159 


1.0164 


1.0170 


1.0175 


1.0181 


1.0187 


79 


11 


1.0187 


1.0192 


1.0198 


1.0204 


1.0210 


1.0217 


1.0223 


78 


12 


1.0223 


1.0229 


1.0236 


1.0242 


1.0249 


1.0256 


1.0263 


77 


IB 


1.0263 


1.0269 


1.0277 


1.0284 


1.0291 


1.0298 


1.0306 


76 . 


14 


1.0303 


1.0313 


1.0321 


1.0329 


1.0336 


1.0344 


1.0352 


75 


15 


1.0352 


1.0360 


1.0369 


1.0377 


1.0385 


1.0394 


1.0402 


74 


16 


1.0402 


1.0411 


1.0420 


1.0429 


1.0438 


1.0447 


1.0456 


73 


17 


1.0456 


1.0486 


1.0475 


1.0485 


1.0494 


1.0504 


1.0514 


72 


18 


1.0514 


1.0524 


1.0534 


1.0544 


1.0555 


1.0565 


1.0576 


71 


19 


1.0576 


1.0586 


1.0597 


1.0608 


1.0319 


1.0630 


1.0641 


70 


20 


1.0641 


1.0653 


1.0664 


1.0876 


1.0387 


1.0699 


1.0711 


69 


21 


1.0711 


1.0723 


1.0735 


1.0747 


1.0760 


1.0772 


1.0785 


68 


23 


1.0785 


1.0798 


1.0810 


1.0823 


1.0837 


1.0850 


1.0863 


67 


23 


1.0863 


1.0877 


1.0890 


1.0904 


1.0918 


1.0932 


1.0946 


66 


24 


1.0946 


1.0960 


1.0974 


1.0989 


1.1004 


1.1018 


1.1033 


65 


25 


1.1033 


1.1048 


1.1063 


1.1079 


1.1094 


1.1110 


1.1126 


64 


26 


1.1126 


1.1141 


1.1157 


1.1174 


1.1190 


1.1206 


1.1223 


63 


27 


1.1223 


1.1239 


1.1256 


1.1273 


1.1290 


1.1308 


1.1325 


62 


28 


1.1325 


1.1343 


1.1361 


1.1378 


1.1396 


1.1415 


1.1433 


61 


29 


1.1433 


1.1452 


1.1470 


1.1489 


1.1508 


1.1527 


1.1547 


60 


30 


1.1547 


1.1566 


1.1586 


1.1605 


1.1625 


1.1646 


1.1666 


59 


31 


1.1666 


1.1686 


1.1707 


1.1728 


1.1749 


1.1770 


1.1791 


58 


32 


1.1791 


1.1813 


1.1835 


1.1856 


1.1878 


1.1901 


1.1923 


57 


33 


1.1923 


1.1946 


1.1969 


1.1992 


1.2015 


1.2038 


1.2062 


56 


34 


1.2032 


1.2085 


1.2109 


1.2134 


1.2158 


1.2182 


1.2207 


55 


35 


1.2207 


1.2232 


1.2257 


1.2283 


1.2308 


1.2334 


1.2360 


54 


33 


1.2360 


1.2386 


1.2413 


1.2440 


1.2466 


1.2494 


1.2521 


53 


37 


1.2521 


1.2548 


1.2576 


1.2304 


1.2632 


1.2661 


1.2690 


52 


38 


1.2690 


1.2719 


1.2748 


1.2777 


1.2807 


1.2837 


1.2867 


51 


39 


1.2867 


1.2898 


1.2928 


1.2959 


1.2990 


1.3022 


1.3054 


50 


40 


1.3054 


1.3086 


1.3118 


1.3150 


1.3183 


1.3216 


1.3250 


49 


41 


1.3250 


1.3283 


1.3317 


1.3351 


1.3386 


1.3421 


1.3456 


48 


42 


1.3456 


1.3491 


1.3527 


1.3563 


1.3599 


1.3636 


1.3673 


47 


43 


1.3673 


1.3710 


1.3748 


1.3785 


1.3824 


1.3862 


1.3901 


46 


44 


1.3901 


1.3940 


1.3980 


1.4020 


1.4060 


'1.4101 ' 


1.4142- 


45 




00' 


50' 


40' 


30' 


20' 


10' 


0- 


Deg. 



NATURAL COSECANT. 



PROVIDENCE, R. I. 



125 



NATUEAL SECANT. 



Deg. 


0' 


10' 


20' 


30' 


40' 


50' 


60' 




45 


1.4142 


1.4183 


1.4225 


1.4267 


1.4309 


1.4352 


1.4395 


44 


46 


1.4395 


1.4439 


1.4483 


1.4527 


1.4572 


1.4617 


1.4662 


43 


47 


1.4662 


1.4708 


1.4755 


1.4801 


1.4849 


1.4896 


1.4944 


42 


48 


1.4944 


1.4993 


1.5042 


1.5091 


1.5141 


1.5191 


1.5242 


41 


49 


1.5242 


1.5293 


1.5345 


1.5397 


1.5450 


1.5503 


1.5557 


40 


50 


1.5557 


1.5611 


1.5666 


1.5721 


1.5777 


1.5833 


1.5890 


39 


51 


1.5890 


1.5947 


1.6005 


1.6063 


1.6122 


1.6182 


1.6242 


38 


52 


1.6242 


1.6303 


1.6364 


1.6426 


1.6489 


1.6552 


1.6616 


37 


53 


1.6616 


1.6680 


1.6745 


1.6811 


1.6878 


1.6945 


1.7013 


36 


54 


1.7013 


1.7081 


1.7150 


1.7220 


1.7291 


1.7362 


1.7434 


35 


55 


1.7434 


1.7507 


1.7580 


1.7655 


1.7730 


1.7806 


1.7882 


34 


56 


1.7882 


1.7960 


1.8038 


1.8118 


1.8198 


1.8278 


1.8360 


33 


57 


1.8360 


1.8443 


1.8527 


1.8611 


1.8697 


1.8783 


1.8870 


32 


58 


1.8870 


1.8959 


1.9048 


1.9138 


1.9230 


1.9322 


1.9416 


31 


59 


1.9416 


1.9510 


1.9606 


1.9702 


1.9800 


1.9899 


2.0000 


30 


60 


2.0000 


2.0101 


2.0203 


2.0307 


2.0412 


2.0519 


2.0626 


29 


61 


2.0626 


2.0735 


2.0845 


2.0957 


2.1070 


2.1184 


2.1300 


28 


62 


2.1300 


2.1417 


2.1536 


3.1656 


2.1778 


2.1901 


2.2026 


27 


.63 


2.2026 


2.2153 


2.2281 


2.2411 


2.2543 


2.2676 


2.2811 


26 


64 


2.2811 


2.2948 


2.3087 


2.3228 


2.3370 


2.3515 


2.3662 


25 


65 


2.3662 


2.3810 


2.3961 


2.4114 


2.4269 


2.4426 


2.4585 


24 


66 , 


2.4585 


2.4747 


2.4911 


2.5078 


2.5247 


2.5418 


2.5593 


23 


67 


2.5593 


2.5769 


2.5949 


2.6131 


2.6316 


2.6503 


2.6694 


22 


68 


2.6694 


2.6883 


2.7085 


2.7285 


2.7488 


2.7694 


2.7904 


21 


69 


2.7904 


2.8117 


2.8334 


2.8554 


2.8778 


2.9006 


2.9238 


20 


70 


2.9238 


2.9473 


2.9713 


2.9957 


3.0205 


3.0458 


3.0715 


19 


71 


3.0715 


3.0977 


3.1243 


3.1515 


3.1791 


3.2073 


3.2360 


18 


72 


3.2360 


3.2653 


3.2951 


3.3255 


3.3564 


3.3880 


3.4203 


17 


73 


3.4203 


3.4531 


3.4867 


3.5209 


3.5558 


3.5915 


3.6279 


16 


74 


3.6279 


3.6651 


3.7031 


3.7419 


3.7816 


3.8222 


3.8637 


15 


75 I 


3.8637 


3.9061 


3.9495 


3.9939 


4.0393 


4.0859 


4.1335 


14 


76 ' 


4.1335 


4.1823 


4.2323 


4.2836 


4.3362 


4.3901 


4.4454 


13 


77 


4.4454 


4.5021 


4.5604 


4.6202 


4.6816 


4.7448 


4.8097 


12 


78 


4.8097 


4.8764 


4.9451 


5.0158 


5.0886 


5.1635 


5.2408 


11 


79 


5.2408 


5.3204 


5.4026 


5.4874 


5.5749 


5.6653 


5.7587 


10 


80 


5.7587 


5.8553 


5.9553 


6.0588 


6.1660 


6.2771 


6.3924 


9 


81 


6.3924 


6.5120 


6.6363 


6.7654 


6.8997 


7.0396 


7.1852 


8 


82 


7.1852 


7.3371 


7.4957 


7.6612 


7.8344 


8.0156 


8.2055 


7 


83 


8.2055 


8.4046 


8.6137 


8.8336 


9.0651 


9.3091 


9.5667 


6 


84 


9.5667 


9.8391 


10.127 


10.433 


10.758 


11.104 


11.473 


5 


85 


11.473 


11.868 


12.291 


12.745 


13.234 


13.763 


14.335 


4 


86 


14.335 


14.957 


15.636 


16.380 


17.198 


18.102 


19.107 


3 


87 


19.107 


20.230 


21.493 


22.925 


24.562 


26.450 


28.653 


2 


88 


28.653 


31.257 


34.382 


38.201 


42.975 


49.114 


57.298 


1 


89 


57.298 


68.757 


85.945 


114.59 


171.88 


343.77 


00 





' 


60' 


50' 


40' 


30' 


20' 


10' 


0' 


Deg. 



NATUKAL COSECANT. 



126 



BEOWN & SHAKPE MFG. CO. 



TABLE OF DECIMAL EQUIVALENT 

OF 8ths, 16ths, 32nds and 64ths of an inch. 



8ths. 

J=..125 

i=.250 
t=.375 

■^=.500 
^==.625 
f=.750 

|=.875 

IGtlis. 

yV=.0625 

y\=.1875 

A=-3125 
tV=.4375 
yV=-5625 . 
i^ = .6875 
if =.8125 
■If =.9375 

32nds. 

ji^ = . 03125 
jV=. 09375 
A= . 15625 
jV=:. 21875 



-3^=. 28125 
ii=. 34375 

i|=. 40625 
If =.46875 
If =.53125 
-If =.59375 
I ^-=.65625 
If =.71875 
If = . 78125 
If =.84375 
if =.90625 
If =.96875 

64ths. 

gL = . 015625 
^\=. 046875 
/^=. 078125 
^V=- 109375 
/j=. 140625 
fi=. 171875 
ff=. 203125 
if =.234375 
ff=. 265625 



f|=. 296875 
|}=. 328125 
f}=. 359375 
If = . 390625 
If =.421875 
||=. 453125 
fi=. 484375 
If =.515625 
If = . 546875 
f2 = . 578125 
11= . 609375 
If = . 640625 
f|=. 671875 
f f = . 703125 
f f = 734375 
11= . 765625 
If = . 796875 
ff=. 828125 
f f = . 859375 
ff=. 890625 
If =.921875 
If =.953125 
If =.984375 



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5i.5 



LIBRARY OF CONGRESS 



021 213 098 9 



k. 



